What You'll Learn
The Concept
For much of American history, searching a person after arrest involved examining physical objects that could fit inside clothing, containers, wallets, or bags. The smartphone changed the scale of that search. A modern phone can potentially reveal years of photographs, private communications, internet searches, financial records, health information, notes, travel, contacts, location history, social networks, and cloud-connected data. Digital evidence has likewise become relevant far beyond cybercrime — NIJ notes that information from computers and mobile devices is now routinely relevant to many categories of criminal investigation.
Historically, police were generally permitted to search certain physical property on an arrestee's person incident to a lawful arrest. The Supreme Court declined to apply that rule mechanically to the digital contents of a cell phone. In Riley v. California, the Court held that police generally must obtain a warrant before searching digital information on a cell phone seized incident to arrest. The decision reflects an important constitutional principle: digital quantity can create a qualitative difference in privacy. A smartphone is physically small but informationally enormous.
Another major issue concerns information held by third parties. Traditional doctrine often provided reduced Fourth Amendment protection for information voluntarily conveyed to third parties. But modern technology creates enormous databases of information generated automatically through routine activity. In Carpenter v. United States, the Supreme Court recognized a limitation on traditional third-party doctrine in connection with historical cell-site location information. Location data can reveal not merely where a person was at one instant but patterns of life over time.
Digital evidence can assist investigators in determining timelines, communication patterns, relationships, location, intent, preparation, knowledge, transactions, concealment efforts, and corroboration or contradiction of statements. The challenge is volume. NIJ has noted that the enormous amount of information stored across computers and mobile devices can overwhelm investigators and laboratories.
Digital evidence is not self-authenticating merely because a computer produced it. Investigators must consider lawful acquisition, preservation, forensic integrity, metadata, extraction methods, access controls, documentation, chain of custody, and interpretation. Digital evidence can be extraordinarily persuasive while simultaneously requiring substantial technical expertise.
Digital technology continuously tests legal doctrines developed in a physical world. Future courts will increasingly confront questions involving cloud storage, geofence information, automated license plate readers, facial recognition, connected vehicles, wearable devices, smart homes, biometric information, and artificial intelligence. The fundamental challenge is balancing legitimate investigative capability with constitutional protections in a society where human activity generates enormous amounts of data.
Real-World Application
Investigators obtain a warrant to search a suspect's phone in connection with a fraud investigation. The phone contains years of messages, financial app records, and location history. Before extracting data, investigators must consider: Does the warrant's scope cover all of this information, or only specific categories? How will they document what was extracted and how? If the phone is cloud-connected, does the warrant extend to cloud data? These questions must be answered before extraction — not after — to preserve the evidence's admissibility and the investigation's integrity.
Why It Matters
For Police Officers
Digital evidence is now central to most serious criminal investigations. Officers who understand the constitutional framework governing digital searches can obtain evidence lawfully and preserve its admissibility — and avoid investigative errors that could compromise prosecutions.
For Students
The intersection of digital technology and constitutional privacy is one of the most rapidly evolving areas of criminal law. Students who understand the foundational cases and the emerging questions will be better prepared for careers in law enforcement, law, or policy.
Think About It
Should long-term location monitoring receive greater constitutional protection than short-term observation?
Does a person's routine use of technology meaningfully constitute consent to governmental access?
Should digital searches require greater particularity in warrant descriptions than traditional searches?
How should courts address surveillance technologies that did not exist when older precedents were decided?
Sources & Further Reading
Riley v. California, 573 U.S. 373 (2014). congress.gov.
Carpenter v. United States, 585 U.S. 296 (2018). congress.gov.
National Institute of Justice. Digital evidence and forensics resources. nij.gov.
National Institute of Justice. Volume of digital evidence in investigations. nij.gov.