A girlfriend hacks her boyfriend’s computer and discovers evidence of tax evasion. She contacts a local law enforcement officer who arrives at her house and looks at the files she found. Without a warrant, the officer opens other files in the same folder the girlfriend had searched. The officer notices another folder labeled “xxx.” He opens the folder and discovers child pornography. The officer seizes the computer based on what he found. The boyfriend is indicted for possession of child pornography and tax evasion. Before trial, the boyfriend moves to suppress all evidence obtained pursuant to the officer’s warrantless search of the computer. What evidence should the judge suppress?

The answer turns on the Fourth Amendment’s private-search exception. Under this exception, a government agent may recreate a search conducted by a private individual so long as the agent does not “exceed the scope” of the prior private search. The question under the existing framework is: at what point did the officer exceed the scope of the prior search—if at all? Was it when he viewed files the girlfriend had not viewed, when he opened files in a different folder, or did he stay within the scope of the girlfriend’s search by only searching the computer’s hard drive? This is what I will refer to as the denominator problem, which asks what courts should use as the unit of analysis to measure the scope of a digital search.

There are at least four competing approaches to the denominator problem, discussed in Part II, and the Supreme Court has provided little guidance on how the private-search doctrine applies to digital searches, resulting in a circuit split. Until this issue is resolved, law enforcement has little guidance on when to obtain a warrant following a private search and can unknowingly subject individuals to unreasonable invasions of privacy, which may result in suppression of relevant evidence. One recent example is United States v. Lichtenberger.