I. Introduction

Judge Learned Hand wrote that it is “a totally different thing to search a man’s pockets and use against him what they contain, from ransacking his house for everything which may incriminate him.”^[1] Reflecting on this statement eighty-eight years later in Riley v. California, the U.S. Supreme Court added this caveat: “If his pockets contain a cell phone, however, that is no longer true.”^[2] Due to the prevalence of digital storage, and the ease with which people can transport their digital lives, without restrictions on digital searches, the government constantly risks the general rummaging Judge Hand warned against, and which the Constitution seeks to prevent.^[3]

The Fourth Amendment protects from unreasonable searches and seizures, but both state and federal courts struggle to define “unreasonable” within the digital context.^[4] The nature of digital searches creates the difficulty. Reasonable searches occur pursuant to a judicially issued warrant or within specific exceptions to the warrant requirement with the intent of limiting the searching official’s discretion.^[5] But warrants and exceptions only suffice to limit physical intrusions into privacy; the primary concern of unreasonableness begins once the intangible search begins.^[6]

Academics and commentators wrangle over whose approach best balances law enforcement needs against individual privacy concerns. The Supreme Court has weighed in only in limited instances,^[7] and until the Court renders an illuminating opinion in the vein of Riley,^[8] those attempting to navigate Fourth Amendment waters travel perilously close to a rocky shoreline. For now, courts must pilot the shoals with whatever tools they find on hand.^[9]

One such tool—and the subject of this Comment—is Professor Orin Kerr’s proposed use restriction on “ongoing seizures,” as suggested in his 2015 article, Executing Warrants for Digital Evidence: The Case for Use Restrictions on Nonresponsive Data.^[10] Under Kerr’s approach, any use of digital data unresponsive to a search warrant qualifies as an unreasonable second seizure.^[11] In the years since his proposal, courts have not rushed to apply Kerr’s “ongoing seizure” restriction, but neither have courts entirely ignored it—with one state adopting it wholesale.^[12] So, too, have scholars considered the merits of Kerr’s “ongoing seizure” approach with mixed reception.^[13] Perhaps a different approach offers a better solution.^[14]

This Comment proceeds as follows: Part II charts the difficulties embedded within digital data searches and explains how Kerr’s “ongoing seizure” limitation proposes to circumvent those difficulties; Part III examines courts’ uses of the Kerr approach; Part IV discusses alternative approaches used by courts and suggested by the academic community; and finally, Part V advocates for the use of evidentiary firewalls.

II. Background

Harold Krent’s 1995 proposal of use restrictions arose from a concern that law enforcement would retain physical evidence for subsequent use following a seizure.^[15] The idea lay dormant until 2011, when Kerr suggested applying use restrictions to data seizures in criminal prosecutions.^[16] Use restrictions have expanded beyond the physical intrusions imagined by Krent and now seek a place within the digital world.^[17]

This Part of the Comment first introduces the trouble created by digital data and how scholars and the Supreme Court have sought to navigate it in the past. Next, using United States v. Morton as an example, it provides a real-world instance where law enforcement’s use of digital search resulted in the discovery of nonresponsive material, implicating the Fourth Amendment privacy concerns at the center of use restrictions. Lastly, it describes how Professor Kerr’s use restriction on “ongoing seizures” proposes to limit law enforcement’s intrusion into individual digital privacy.

A. Unique Fourth Amendment Challenges Presented by Digital Searches

Digital searches present unique problems not present in the physical world and need novel restrictions to avoid a government’s trend toward tyranny.^[18] The U.S. Supreme Court confronted this novelty for the first time in Riley.^[19] The Court combined two cases in which cell phones seized during searches incident to the arrests yielded information law enforcement used to facilitate additional charges or subsequent searches.^[20] Both trial courts refused to suppress the evidence that led to the eventual convictions.^[21] The Supreme Court acknowledged the privacy concerns implicated by the modern cell phone’s “immense storage capacity.”^[22] In its response to Judge Hand’s ruminations on the difference between a man’s pocket and his house, the Court noted that a “phone not only contains in digital form many sensitive records previously found in the home; it also contains a broad array of private information never found in a home in any form—unless the phone is.”^[23] In light of the privacy risk cell phones pose, the Court required law enforcement to obtain a search warrant before searching a cell phone, even when seized incident to arrest.^[24]

Digital storage has expanded in the years since Riley. A one-terabyte thumb drive holds the data equivalent of 65 million printed pages, 100 million e-mails, 16 million images, and 675 million text messages.^[25] The Second Circuit noted that it is possible to purchase a storage device containing the equivalent of “16 billion thick books.”^[26] However, binary data means nothing to the human mind, and a computer’s organizational structures do not reflect the tidy images evoked by the interface software’s use of files and folders.^[27] Digital evidence often cannot be fully known until it is opened.^[28]

Recognizing the complications in finding a metaphorical needle in a digital haystack, Congress authorized courts to warrant overseizure.^[29] A warrant first authorizes a search of the physical location and the seizure of the digital storage devices described in the application and supporting affidavits.^[30] Following the seizure, in an attempt to conform with the Fourth Amendment’s particularity requirement, law enforcement renders data into a perfect electronic copy that a forensic examiner later analyzes to separate data responsive to the warrant from unresponsive data.^[31] But courts often permit law enforcement to search the data anywhere that evidence relevant to the inquiry might be found, if only to rule out data corruption or virus intrusion.^[32] Courts have split on when—and even if—a digital search ever becomes unreasonable for subjective searches beyond a warrant’s scope, leading to encounters with nonresponsive data.^[33] In a typical physical search, nonresponsive evidence in plain view falls within an exception to the Fourth Amendment.^[34] But whether the plain view exception should apply in the digital context remains unclear.^[35] Exposure to nonresponsive data raises the reasonableness question that Kerr and other scholars have attempted to answer.

B. The Fifth Circuit Circumvented Unreasonableness in United States v. Morton^[36]

The digital and highly sensitive nature of child pornography in the modern world can potentially skew jurisprudence in favor of the government.^[37] Gray-area digital searches force courts to choose between letting potential child predators go free or treading on individual privacy interests. The Fifth Circuit confronted this issue in United States v. Morton.^[38]

Morton consented to a search of his van after being pulled over for speeding, and Texas Department of Public Safety (DPS) Troopers found ecstasy, marijuana, and a glass pipe within.^[39] More concerning to the troopers, Morton’s van contained “children’s school supplies, a lollipop, 14 sex toys, and 100 pairs of women’s underwear.”^[40] They arrested Morton for drug possession.^[41]

In a warrant application to search three cell phones found in Morton’s van, the troopers only described evidence of Morton’s criminal drug activity; they did not mention suspicion of child predation or exploitation.^[42] The subsequent search uncovered sexually explicit images of children.^[43] A second warrant to search for child pornography, based on probable cause arising from the first search, produced “19,270 images of sexually exploited minors.”^[44] Morton’s motion to suppress the images failed; he pled guilty to child pornography charges conditional upon appeal and the court sentenced him to nine years in prison.^[45]

On appeal to the Fifth Circuit, a three-judge panel held that because the first warrant lacked sufficient probable cause to search the phones for drug-related evidence, any further evidence originating from that search was “fruit of the poisonous tree”; thus, the trial court erred by not suppressing it.^[46] On a rehearing en banc, the full Fifth Circuit vacated the panel opinion and affirmed the trial court’s decision, basing its holding on the officers’ good faith reliance on the magistrate’s warrant.^[47]

A five-judge concurrence recognized the echoes of Riley. The concurrence expressed concern that even “with such a meager showing, officers would gain unfettered access to all of ‘the privacies of life.’”^[48] The concurring judges asked whether Kerr’s use restriction might create the right solution to a situation like Morton’s, noting that one state had already applied Kerr’s approach.^[49] The concurrence concluded by observing that the Supreme Court should—and likely would—make a Riley-like adjustment to Fourth Amendment jurisprudence in the future.^[50] Unfortunately, the Court rejected Morton’s petition for a writ of certiorari, so it does not appear that a “Riley moment” will soon arrive.^[51]

C. Orin Kerr’s “Ongoing Seizure” Use Restriction

Given the right circumstances, Kerr believes the Supreme Court will reevaluate an old paradigm and, considering new facts, “adopt a new rule to restore the equilibrium struck by the old rule in the old factual environment.”^[52] The plain view exception no longer suffices—it produces results too close to general rummaging.^[53] However, eliminating the plain view exception in digital searches fails to solve the problem. The exception applies to seizing evidence in plain view; and because law enforcement has already seized digital evidence when viewed, plain view can no longer apply.^[54] The doctrinal shift, Kerr argues, should come from use restrictions imposed on the data that is nonresponsive to the warrant during a comprehensive search following an overseizure.^[55]

Kerr suggests that the use of nonresponsive files “violates the Fourth Amendment in a two-stage computer search because it renders the ongoing seizure of the nonresponsive files constitutionally unreasonable.”^[56] He points to United States v. Jacobsen, in which law enforcement opened a lawfully seized package containing cocaine and destroyed a small portion of the cocaine to test it.^[57] While the Supreme Court held this search reasonable under a balancing test that weighed the “nature and quality of the intrusion” against the important “governmental interests alleged to justify the intrusion,” the Court indicated that a secondary seizure is never presumptively reasonable.^[58] Building on this, Kerr argues that courts should consider the subsequent use of lawfully seized nonresponsive digital data presumptively unreasonable.^[59] Subsequent use transforms the “nature and quality” of the seizure into the prohibited general warrant and eliminates the Fourth Amendment’s particularity requirement.^[60] Further, subsequent use offends the proportionality principle established in Terry v. Ohio for failing to remain “reasonably related in scope to the circumstances which justified the interference in the first place.”^[61]

An “ongoing seizure” analysis asks whether further use satisfies Terry.^[62] Kerr provides a list of situations in which this application results in an unreasonable secondary seizure. First, utilizing nonresponsive data no differently from data cited in the warrant violates the Terry requirement.^[63] Second, additional warrants based on probable cause created by nonresponsive data create a similar violation, rendering the difference between first and subsequent warrants into nothing more than paperwork obstacles.^[64] And third, disclosing nonresponsive data to the public renders it unreasonable—especially when the information might reveal the individual’s “prurient interests or personal foibles.”^[65]

How might the Fifth Circuit have ruled in Morton if the court had considered Kerr’s “ongoing seizure” use restriction beyond a mention in the concurrence?^[66] First, in line with Riley, troopers seized Morton’s cell phones pursuant to a search incident to arrest and did not begin a search until after obtaining a warrant.^[67] At this point, the facts do not collide with Kerr’s use restriction. However, because the troopers obtained a search warrant seeking only data indicative of drug trafficking, exposure to any data nonresponsive to that warrant would collide.^[68] The moment the troopers encountered images of child exploitation, Kerr’s “ongoing seizure” restriction would be triggered, making any subsequent use of that data unreasonable under the Fourth Amendment.^[69]

Had an “ongoing seizure” restriction existed at the time, the troopers would not have had recourse to seek a second warrant.^[70] And even if a magistrate had issued a second warrant, any successive court reviewing the constitutionality of the second warrant would have to conclude that it violated the Fourth Amendment’s prohibition against unreasonable searches and seizures.^[71]

In Morton, the en banc Fifth Circuit upheld the trial court’s denial of Morton’s motion to suppress on the basis that the troopers—in their first search of Morton’s phones—acted in good faith reliance on the warrant.^[72] But with Kerr’s “ongoing seizure” use restriction in place, when determining good faith, the Fifth Circuit would have found the second warrant a violation of the Fourth Amendment and prevented officers from converting a “traffic stop that produced evidence of a marginal offense” into “an excuse to gain unfettered access to a device saturated with personal, private information.”^[73] Morton might still have found himself convicted, but only of minor drug possession, not for possession of child pornography.

As discussed below, the one court to have adopted Kerr’s approach did so with mixed results.^[74] Kerr even expressed regret at one result, which allowed a father who had allegedly shaken his infant to death to go free.^[75]

III. Among Courts, Kerr’s Use Restriction on “Ongoing Seizures” has Received Limited Welcome.

Kerr’s use restriction has seen little adoption. At the time of Kerr’s publication, the Second Circuit appeared to adopt an “ongoing seizure” approach—the only federal court to do so—but it backtracked. Further, organizations dedicated to protecting individual liberties and digital freedom have petitioned the federal courts to consider Kerr-style restrictions. They have only met silence. While one state court has adopted a version of this use restriction, most have not considered it, and those that have, have either ignored or rejected the approach.

This Part reviews the application of Kerr’s use restriction—if any—within the federal and state court systems.

A. Federal Courts

Though some judges have taken note of Kerr’s “ongoing seizure” approach, federal courts have generally ignored it. In a case built on the subsequent search of previously seized data, a three-judge panel from the Second Circuit applied what Kerr described as “a particularly strong version of the ongoing seizure approach.”^[76] However, any potential adoption remained short-lived; shortly before Kerr’s article was published, the Second Circuit granted a rehearing en banc.^[77] As with the Fifth Circuit in Morton, the Second Circuit decided the appeal on the good faith exception and declined to evaluate the merits of the Fourth Amendment challenge.^[78] Regarding the application of the “ongoing seizure” approach, the en banc opinion found “no scholarly consensus on the complicated questions implicated in this case” and advised caution as “the most appropriate approach.”^[79] The Second Circuit has yet to adopt Kerr’s approach.

District courts have declined to engage with the “ongoing seizure” use restriction. A Nevada district court mentioned Kerr’s approach as a “workable solution” for “appropriately narrow warrants” and the subsequent use of data; however, it did not apply the solution as the warrant under its consideration proved “fatally overbroad.”^[80] A South Dakota district court magistrate judge referenced Kerr’s “ongoing seizure” use restriction in recommending that “the plain view exception to the warrant requirement be held not applicable in searches of digital evidence.”^[81] However, when the district court judge modified the opinion before adoption, that judge omitted the Kerr reference.^[82]

Similarly, federal appellate courts have remained mute when criminal appellants invoke Kerr’s use restriction. When petitioned to weigh in on the issue of digital searches and to issue a “Riley moment,” as Kerr prompted, the Supreme Court remained silent, denying certiorari on the matter.^[83] As amici, the Electronic Frontier Foundation (EFF) and the American Civil Liberties Union (ACLU) asked the Ninth Circuit to block evidence of child pornography found on a cellphone pursuant to a search conducted under a Foreign Intelligence Surveillance Act (FISA) warrant because it did not pertain to foreign intelligence.^[84] The Ninth Circuit thanked the EFF and the ACLU “for their thought-provoking briefing,” admitting the situation came close to “the exact abuses against which the Fourth Amendment was designed to protect,” but found no error.^[85]

At the time of this Comment’s writing, no federal court has adopted Kerr’s “ongoing seizure” use restriction. However, two years before Kerr’s article’s publication, the Ninth Circuit arrived at a close facsimile, holding that “[t]he government’s seizure of items beyond the terms of [a digital search] warrant violated the Fourth Amendment.”^[86] The five-judge concurrence in Morton remains the strongest mention of Kerr’s approach to appear in a standing federal court opinion.^[87]

B. State Courts

In 2018, Oregon adopted the “ongoing seizure” use restriction in State v. Mansor, heavily rooting its legal theory in Kerr’s scholarship.^[88] There, police drafted a narrow warrant seeking Mansor’s internet search history for the day his infant son died.^[89] Police later added Mansor’s e-mail to the list and provided FBI forensic analysts with an expanded list of search terms and a wider timeframe in which to search, all without obtaining an additional warrant.^[90] The analysts further added their own search terms.^[91] The subsequent report detailed a comprehensive history of Mansor’s entire digital life, going back six years before the infant’s birth.^[92] The trial court denied Mansor’s motion to suppress on the basis that the digital data fell within the plain view exception; a jury convicted him on all charged counts.^[93]

The Oregon Supreme Court rejected the holdings of both lower courts.^[94] Instead, the state high court relied on Kerr’s proposal to hold that data nonresponsive to a warrant should be suppressed.^[95] Kerr applauded the state’s adoption—while simultaneously lamenting that a poorly drafted warrant vacated a child abuser’s conviction for murder. But, he added this caveat: because the court decided Mansor under the Oregon Constitution’s search and seizure provision, “the decision is interesting and relevant more by way of illustration than precedent.”^[96]

But even the Mansor holding has come under some attack when applied without nuance. The Oregon Court of Appeals questioned whether data obtained lawfully—but which fell outside the warrant’s scope—fell within Mansor’s prohibitions.^[97] Post-Mansor cases had not provided an answer, so the court resorted to reading tea leaves.^[98] It reasoned that, in light of Mansor, the Oregon Supreme Court would likely prohibit any use of the data in question.^[99] As a result, law enforcement could not use the data obtained during a lawful search that fell outside the warrant.^[100] Nor could it use that data to develop probable cause to obtain a second warrant or to further additional lines of investigation.^[101] The concurrence argues that the Mansor line of cases requires law enforcement to “turn a blind eye to criminal activity that lawfully comes to their attention” and hopes the Oregon Supreme Court will clarify its prohibitions on use.^[102]

No other states have adopted Oregon’s approach. Following Mansor, the Indiana Court of Appeals observed that an officer’s failure to abide by a warrant’s date restriction rendered digital evidence outside that warrant’s scope inadmissible.^[103] However, the nonresponsive evidence did not factor in either of the trial court’s rulings in that case, and played no part in the appellate court’s holding.^[104] In another case, the Supreme Court of Wisconsin registered no reaction to an amicus filing by the ACLU suggesting the court adopt Mansor’s application of Kerr’s use restriction.^[105] Similarly, the Superior Court of Pennsylvania, Middle District, remained silent to the suggestion it should apply a Mansor-style use restriction to any evidence exceeding a search warrant.^[106] In a separate case, the Supreme Court of Pennsylvania declared a warrant void for lack of probable cause without engaging with the use restrictions suggested in an amicus brief.^[107]

While Oregon stands alone in adopting Kerr’s “ongoing search” use restriction, nothing indicates whether this results from a lack of the right facts or from a reluctance of the courts to implement such a restrictive approach.

IV. Legal Commentators Offer Competitive Approaches to Protect Privacy Interests from Intrusive Digital Searches

Legal commentators have offered no more than a lukewarm reception of Kerr’s use restriction against “ongoing seizures.” Some have offered competitive solutions, while others have addressed specific flaws in the approach. Consensus remains elusive. This Part first describes the issues arising from post hoc review. It next addresses how ex ante restrictions potentially avoid pitfalls presented by Kerr’s post hoc approach. It concludes with an analysis of how Kerr’s “ongoing seizure” use restriction creates potential conflicts with governmental obligations required under Brady v. Maryland.

A. Post Hoc Problems

The post hoc nature of Kerr’s use restriction presents prosecutors and courts with difficult choices. Because Kerr’s approach limits the use of data found outside the scope of warrants, instituting it provides an incentive to broadly expand the scope of warrant applications.^[108] Further, law enforcement can freely use evidence of other crimes discovered within the data responsive to the warrant.^[109] Courts then find themselves in a position of evaluating the totality of circumstances to determine the reasonableness of the search,^[110] or in the case of Mansor, limiting the construction of the warrant post hoc.^[111]

But even in Mansor, had law enforcement broadened the initial warrant or properly sought a second one upon creation of new probable cause, that court would not have had occasion to institute Kerr-style use restrictions.^[112] Ultimately, if law enforcement searches digital evidence within the reasonable limitations a warrant provides, any evidence of additional crimes appearing within that scope requires additional warranted permission from a magistrate to remain within the Fourth Amendment—a practice used by the officers in Morton.^[113]

Relying on post hoc review can create uncertainty for law enforcement and the courts.^[114] As Kerr noted in his response to Mansor, the investigating officers probably did not expect the court to construe their warrant as narrowly as it did.^[115] Additionally, as seen in Morton, courts often deal with digital searches in the context of child pornography cases.^[116] Because courts exhibit a reluctance to release those convicted of creation or possession of child pornography, caselaw in this area favors the government.^[117] Encountering factual situations starkly different from the child pornography context might leave courts looking for other approaches that more favorably solve the digital search problem.

B. Ex Ante Restrictions

Noting the difficulties arising out of the post hoc nature of Kerr’s approach, ex ante restrictions seek to eliminate constitutional violations before they happen. FISA courts use a procedure arising from Title III wiretaps called minimization.^[118] Minimization “is any set of procedures ‘reasonably designed in light of the purpose and technique’ of information collection ‘to minimize the acquisition and retention, and prohibit the dissemination,’ of information whose collection is not authorized.”^[119] Following the model of FISA courts, magistrates would require the government to propose rules to the court governing the collection and sifting of digital data.^[120] Magistrates and the government work hand-in-hand to tailor governmental needs specific to each investigation while balancing individual privacy issues.^[121] Following seizure, FISA courts insulate data by utilizing separate analysts to sift for data responsive to the warrant without ever exposing the evidence to investigators directly responsible for the case.^[122] Upon finding evidence of additional crimes, investigators can always return to the magistrate to adjust the warrant’s scope.^[123]

Additionally, this approach removes the unfortunate side effects of Kerr’s post hoc approach. First, delineating clear rules provides law enforcement with predictability and prevents relying on guesswork as to what each court regards as appropriate.^[124] Second, the plethora of post hoc appeals challenging digital searches arising in child pornography cases create a disproportionate body of caselaw relying on unsympathetic defendants.^[125] Third, the cooperative nature of minimization techniques between law enforcement and the magistrate eliminates over-reliance on the good-faith exception to circumvent constitutional violations.^[126] Minimization provides the benefit of utilizing the FISA format, already familiar within the court system, applied via ex ante restrictions already used by magistrates.^[127]

C. Brady Concerns Arising from Kerr’s “Ongoing Seizure” Use Restriction

Regardless of ex ante or post hoc restrictions, the “ongoing seizure” approach creates a conflict arising from the government’s Brady obligations.^[128] This “Digital Disclosure Trilemma,” as one commentator describes it, creates a paradox of obligations for the government.^[129] First, under Brady, the government must disclose all exculpatory evidence within its possession—including evidence seized but outside the scope of the search warrant.^[130] Second, in turning over evidence, the government must comply with a discovery statute restricting it from turning over “any property or material that constitutes child pornography.”^[131] Without reviewing all the digital evidence within its possession, the government cannot satisfy its Brady obligations.^[132] However, reviewing all the digital evidence exposes the government to nonresponsive data and risks falling afoul of Kerr’s “ongoing seizure” use restriction, eliminating the government’s ability to properly develop probable cause for additional crimes contained within the digital evidence.^[133]

The Fourth Amendment remains the guiding star here, and though little agreement exists within the courts and between commentators, one throughline exists. The next Part discusses a solution: increased use of evidentiary firewalls.

V. Utilizing an Evidentiary Firewall Provides the Desired Fourth Amendment Safeguards

Creating an evidentiary firewall requirement will provide the simplest way to protect the Fourth Amendment right to individual privacy without substantially burdening the government in its effort to execute its mandate. This Part advocates building on similar formats that already exist within FISA, attorney-client, and government contexts. Building on existing formulas prevents courts and law enforcement from having to create a new system out of whole cloth. Additionally, it addresses how the development of computer-assisted searches will further reduce the need for human investigators to execute interactive data searches, helping solve potential Brady issues. It concludes by discussing how the use of an evidentiary firewall would have affected Morton.

A. Applying Already Existing Evidentiary Firewall Procedures to Digital Searches

The evidentiary firewall concept already exists within governmental protocols for occasions when law enforcement searches sensitive or privileged materials.^[134] As discussed above, FISA courts apply similar measures to mass-collected data in the national security context.^[135] Applying a similar insulating approach to criminal investigations following a Rule 41 overseizure prevents investigators from directly accessing nonresponsive data.^[136]

The Department of Justice (DOJ) Justice Manual illustrates how this process works in the context of investigating an attorney.^[137] First, law enforcement should write the warrant “to minimize the need to search and review privileged material to which no exception applies.”^[138] Second, a privilege team consisting of non-investigatory agents or lawyers follows instructions “designed to minimize intrusion into privileged materials,” ensuring the team “does not disclose any information to the investigation/prosecution team unless and until so instructed by the attorney in charge of the privilege team.”^[139]

Courts prefer three methods concerning privileged digital materials.^[140] First, in camera review; second, the court can appoint a special master; and third, the court can use a filter team that establishes what the DOJ terms an “ethical wall” in privilege situations.^[141] Of the three, filter teams perform the work quickest, though some courts express reluctance to use them.^[142] Ultimately, as long as filter team procedures “adequately protect[] the defendants’ rights and no prejudice occur[s],” then courts have generally approved of their use.^[143]

Utilizing an evidentiary firewall solves many of the problems encountered with Kerr’s “ongoing seizure” use restriction and the alternative solutions proposed by other commentators. First, the firewall provides insulation for the investigators—they will only ever see the evidence provided to them by a filter team.^[144] This reduces the requirement for the circuit courts to construct broad rules based on the adherence of investigators to existing jurisprudence; instead, it reduces the review to whether law enforcement acted within the filter team protocols.^[145] The Supreme Court should provide the review standard, removing the need for magistrates to apply ex ante restrictions. Kerr’s post hoc review preference would no longer rest on arbitrary magistrate decisions but review reasonableness in the context of the ultimate ex ante protocols—U.S. Supreme Court rulings.

Second, an evidentiary firewall approach alleviates the concern that jurisprudence in this area disproportionately originates in cases involving child pornography.^[146] Review in these cases becomes fact specific and no longer broadly addresses the area of digital searches.^[147] And third, because this approach puts the onus on investigators and the filter team to follow either judicial orders ex ante or Supreme Court holdings, it removes the need for appellate courts to rely on the good-faith exception to protect society from child predators.^[148]

B. Utilizing Computer Algorithmic Binary Searches to Solve the Brady Problem

The continued development of technology in this sphere can assist filter teams on the non-investigatory side of the firewall. Similar to how courts view narcotics field tests and drug dog searches, applying the principle of binary searches to computer-assisted digital searches further provides a Fourth Amendment buffer.^[149] The Supreme Court has held that evidence of criminal contraband does not fall within the scope of a “legitimate privacy interest.”^[150] Because a binary test only reveals the presence or lack of contraband, any binary test conducted where an officer is lawfully present that reveals “no information other than [contraband] no individual has any right to possess does not violate the Fourth Amendment.”^[151]

On the filtration side of the firewall, computer algorithms can mine the data and only reveal digital evidence comporting with the search warrant’s particularity requirements.^[152] Additionally, law enforcement could opt to only search the data for elements of probable cause; once armed with probable cause, law enforcement could seek a warrant to observe the data.^[153] Because the nature of these searches remains binary, no Fourth Amendment implications exist.^[154]

Employed together, evidentiary firewalls and binary searches can effectively neutralize the Brady concerns illustrated above.^[155] First, by running an algorithmic child pornography-directed binary search, the filter team would potentially satisfy the statutory requirement against turning over child pornography by segregating any data that falls within the statute.^[156] Additionally, because the binary search does not fall within the Fourth Amendment, the government never becomes aware of potentially exculpatory evidence beyond that identified as responsive to the warrant, limiting Brady liability and reducing the digital evidence it must turn over.

Binary searches aside, a filter team reviewing materials would still preclude Brady issues. The team, acting within the warrant’s scope, would sift digital data into its various categories: Brady materials, data responsive to the warrant, and data nonresponsive to the warrant. New probable cause or prosecutorial action would be restricted, only arising from the materials sifted into the responsive category, satisfying Kerr’s concerns with intrusion into Fourth Amendment privacy interests. Under a Rule 41 motion, pursuant to a judge’s ex ante order or predicated on any future U.S. Supreme Court holdings, materials nonresponsive to the warrant can be returned.^[157] The Ninth Circuit has already grappled with this and applied a system of evidentiary firewalls; by segregating data and instituting filter team search protocols, law enforcement serves the Fourth Amendment by protecting individual privacy interests.^[158] Perhaps this provides a roadmap for the Court to follow.

C. Morton and the Evidentiary Firewall

Had the Texas DPS Troopers utilized an evidentiary firewall during their investigation of Morton, they would have only had access to evidence from his phones directly relating to the original warrant. That warrant only allowed searching for evidence of narcotics trafficking or possession.^[159] A filter team would have limited the evidence it provided to the investigatory team to that approved under the warrant—evidence of drug possession or trafficking.

However, this does not mean Morton would have automatically gone free. Already suspicious of Morton’s behavior based on the presence of “children’s school supplies, a lollipop, fourteen sex toys, and one hundred pairs of women’s underwear in the vehicle,” the troopers would not have had the option to engage in a pretextual search of Morton’s phone.^[160] Instead, the troopers would have needed to properly develop probable cause before obtaining a warrant to search his cell phones for child pornography. While this might add an investigatory burden on law enforcement in the future, this is the balance the Fourth Amendment requires.

VI. Conclusion

Kerr’s “ongoing seizure” use restriction has not gained traction within the court systems or the body of legal scholarship surrounding the Fourth Amendment. As seen in Ganias and Morton, courts often rely on the good-faith exception to circumvent opportunities where a use restriction might apply. After Mansor, Kerr indicated that a better-written warrant application would have precluded the Oregon high court’s opportunity to restrict use. Kerr admitted that law enforcement in Mansor developed enough probable cause from its first search to obtain a second warrant and broaden the scope. And finally, considering the government’s Brady obligations, any strong enforcement of Kerr’s approach would remove the possibility of creating new independent probable cause during a Brady examination. Under Kerr’s “ongoing seizure” use restriction, any exposure to additional criminal material becomes instantly suppressible, crippling subsequent investigations before they even start.

Instead, courts should rely on evidentiary firewalls via filter teams and algorithmic binary searches. Utilizing this approach removes the reliance on the good-faith exception, allows the body of digital search jurisprudence to develop free from a disproportionate balance of child pornography cases, and creates an avenue by which the government can easily satisfy its Brady requirements. The practice is already in use in governmental and privilege contexts where enhanced privacy interests exist. The Ninth Circuit has adopted a similar approach and has shown how it can protect privacy interests without sacrificing the government’s investigatory mandate. Digital data continues to expand its presence in the courts, and as Kerr noted, another Riley moment is due from the Supreme Court. But, with the Court denying certiorari in Morton v. United States, uncertainty remains.

Frank Chambers