Seminar Transcript | Tech-Law Salon: Trends in U.S. Technology-Assisted Investigation

Seminar Transcript

This session focuses on *Carpenter*, a U.S. Supreme Court decision issued three years earlier concerning historical cell-site location information (CSLI). CSLI is generated when a mobile phone connects with cellular towers and can be used to reconstruct the phone user's approximate location. Whether law enforcement must obtain a search warrant for this type of information can be understood only against the background of earlier Fourth Amendment cases.

Basic U.S. Legal Framework

At a high level, U.S. search-and-seizure doctrine asks whether government conduct constitutes a Fourth Amendment "search" and, if so, whether the search is reasonable. Searches ordinarily require a warrant supported by probable cause, subject to recognized exceptions, including certain exigent circumstances. Technology does not displace that constitutional framework; the difficult question is when a technologically assisted investigative method triggers it.

Different Evidentiary Thresholds

U.S. law uses different burdens or thresholds in different contexts, including reasonable suspicion, probable cause, preponderance of the evidence, clear and convincing evidence, and proof beyond a reasonable doubt. Probable cause is the threshold generally associated with issuance of a search warrant; preponderance of the evidence is a common civil burden, while proof beyond a reasonable doubt is the criminal-trial standard.

U.S. Case Law Before *Carpenter*

*Olmstead*

The historical starting point is *Olmstead v. United States*. In the era of *Olmstead*, Fourth Amendment analysis was closely tied to property concepts and physical intrusion. The wiretaps at issue had been installed without physically entering the defendants' premises, and the Court therefore found no constitutionally protected search or seizure. The decision illustrates the older trespass- and property-centered approach to the Fourth Amendment.

* Fourth Amendment: The Fourth Amendment to the U.S. Constitution protects against unreasonable searches and seizures and provides that warrants may issue only upon probable cause, supported by oath or affirmation, and with particularity as to the place to be searched and the persons or things to be seized.

That property-centered approach did not remain the exclusive test. Later cases, most importantly *Katz*, recognized that Fourth Amendment protection is not limited to physical trespass into a constitutionally protected place. Government interception of private communications may constitute a search even without physical entry.

*Katz*

In *Katz v. United States*, the defendant used a public telephone booth, and FBI agents attached an electronic listening and recording device to the outside of the booth. The Court held that the Fourth Amendment was implicated even though agents had not physically entered the booth. The decision is famously associated with the principle that "the Fourth Amendment protects people, not places" and with Justice Harlan's concurrence articulating what later became the reasonable-expectation-of-privacy framework.

The Door Opened by *Katz*

*Katz* moved Fourth Amendment analysis beyond a purely physical conception of protected space. Under the reasonable-expectation-of-privacy formulation, the inquiry considers whether a person exhibited an actual expectation of privacy and whether society is prepared to recognize that expectation as reasonable. That expansion also created recurring questions about what expectations count as reasonable as technology and social practices change.

U.S. Case Law Before *Carpenter* (2)

*Berger* - Statutory Wiretapping

*Berger v. New York* involved electronic surveillance authorized under a New York statute. The Supreme Court held the statute constitutionally deficient because its authorization and safeguards did not satisfy Fourth Amendment requirements. The broader lesson for technology-assisted investigation is that a legislature cannot avoid constitutional search-and-seizure protections simply by creating a statutory surveillance mechanism with a lower or looser threshold than the Constitution permits.

U.S. Case Law Before *Carpenter* (3)

*Kyllo* - Technology "Not in General Public Use"

In *Kyllo v. United States*, law-enforcement officers used a thermal-imaging device from outside the defendant's home and detected heat patterns associated with indoor marijuana cultivation. The thermal-imaging information was then used in seeking a warrant. The Supreme Court treated the use of the device itself as a Fourth Amendment search.

One important point in *Kyllo* is the Court's recognition that technological development can affect the practical scope of privacy protected by the Fourth Amendment. Constitutional protection cannot be understood as though advances in surveillance technology had no effect on what government can learn without physically entering a protected space.
The Court held, in substance, that using sense-enhancing technology to obtain information about the interior of a home that could not otherwise have been obtained without physical intrusion constitutes a search-at least where the technology is not in general public use. The home remained central to the Court's reasoning.

The Door Opened by *Kyllo*

*Kyllo* therefore added another consideration to technology cases: the capabilities and general availability of the investigative technology itself. Together with *Katz*, the case helped shape modern debates over a reasonable expectation of privacy (REP), although the doctrines do not reduce to a single mechanical test.

U.S. Case Law Before *Carpenter* (4)

*Jones* - The Trespass Doctrine Survives

In *United States v. Jones*, law-enforcement officers physically attached a GPS tracking device to a vehicle and used it to monitor the vehicle's movements. The Supreme Court held that this physical intrusion to obtain information constituted a Fourth Amendment search. Importantly, *Jones* did not discard *Katz*; it confirmed that property-based trespass remains an independent route to finding a search alongside reasonable-expectation-of-privacy analysis.

Implications of *Jones*

After *Jones*, technology-assisted investigation can implicate the Fourth Amendment through more than one doctrinal route. A physical intrusion into constitutionally protected property to obtain information may itself constitute a search. Separately, even without trespass, government surveillance can constitute a search where it infringes a reasonable expectation of privacy. These overlapping approaches remain central to analysis of newer investigative technologies.

* Supplement: The Third-Party Doctrine. Under cases including *Smith v. Maryland* and *United States v. Miller*, information voluntarily conveyed to a third party has traditionally received reduced Fourth Amendment protection. Telephone dialing records and bank records were classic examples. The doctrine became increasingly difficult to apply mechanically as digital services caused enormous quantities of personal information to be held by third parties.

The *Carpenter* Case

In *Carpenter*, the government obtained historical CSLI from wireless carriers under a federal statutory order requiring less than probable cause. The government argued that, because the records were held by third parties, the traditional third-party doctrine meant no warrant was required. The Supreme Court disagreed with a categorical application of that doctrine to historical CSLI and held that acquisition of the records at issue constituted a Fourth Amendment search requiring a warrant supported by probable cause. The Court emphasized the distinctive character of cell-phone location records and expressly declined simply to extend *Smith* and *Miller* to the new context.

Analyzing the *Carpenter* Rationale (1)

The "Unique Nature" of CSLI

The speaker focused first on the comprehensiveness of historical CSLI. Earlier reasonable-expectation-of-privacy cases often asked about the nature of a particular place or item of information. *Carpenter*, by contrast, gave weight to the amount and aggregation of location information. The speaker therefore asked whether the decision had begun to treat the quantity and comprehensiveness of collected data as part of the privacy analysis rather than looking only at each individual data point.

Analyzing the *Carpenter* Rationale (2)

The speaker next compared CSLI with conventional visual surveillance and the GPS tracking at issue in *Jones*. In theory, police can observe a person's movements on public roads, but sustained physical surveillance is costly and difficult. Cell-phone location records make long-term tracking dramatically easier and cheaper. The speaker questioned how that practical difference should fit into Fourth Amendment doctrine, because the ease and efficiency of an investigative technique had not traditionally operated as an independent constitutional test. He also stressed that *Jones* itself had been resolved on physical-trespass grounds, whereas *Carpenter* involved no government trespass on the defendant's property.

Analyzing the *Carpenter* Rationale (3)

The Court also emphasized the ubiquity of cell phones and the increasingly precise nature of CSLI. The speaker noted a tension with *Kyllo*: there, technology not in general public use supported greater constitutional protection, while *Carpenter* treated the near-universal use of cell phones as one reason location records were especially revealing and difficult to avoid. He also questioned how courts should account for rapidly improving precision-CSLI historically was less exact than GPS, but technological development can narrow that gap.

Uncertainty After *Carpenter* (1)

After *Carpenter*, several competing interpretations are possible, and it remains uncertain which direction later Supreme Court cases will take:

1. Trespass and reasonable expectation of privacy remain the two principal doctrinal routes, but REP analysis now may also require consideration of:
   (1) the comprehensiveness emphasized in *Carpenter*, the practical ease of surveillance, and the effects of long-term tracking;
   (2) the volume and aggregation of information;
2. A broader defense-oriented reading is that comprehensive digital information may be emerging as a distinct third dimension of Fourth Amendment analysis in addition to trespass and REP.
3. A narrower prosecution-oriented reading is that *Carpenter* is a limited exception tied to the distinctive characteristics of historical CSLI and should not be generalized broadly.

Uncertainty After *Carpenter* (2)

What can be said with confidence is that the traditional trespass doctrine remains alive. The harder questions are whether *Carpenter* substantially weakened the third-party doctrine, merely refined reasonable-expectation-of-privacy analysis, or introduced a new emphasis on aggregation and comprehensiveness. Future cases will also have to decide whether factors highlighted in *Carpenter*-including long-term tracking, practical ease, ubiquity, and informational depth-should affect analysis of other technology-assisted investigative methods.