State v. Gasper, 30 N.W.3d 367 (Wis. 2026)
Sometimes police are not the first ones to find evidence. Sometimes a computer using artificial intelligence does.
Modern child-exploitation investigations often begin with a CyberTip from a technology company. Social media and cloud storage platforms routinely scan uploaded files for known child sexual abuse material (CSAM). When a match appears, the company must report it to the National Center for Missing and Exploited Children (NCMEC), which then forwards the report to law enforcement.
That is how this case began. Snapchat’s automated system matched a 16-second video uploaded from Michael Gasper’s account with known CSAM. The alert was made possible by Microsoft’s PhotoDNA technology, which compares the digital fingerprints (or “hash values”) of uploaded file to a database of previously identified illegal images. No human employee at Snapchat watched the video. Rather, the software flagged it automatically.
Snapchat sent the report to NCMEC, which forwarded it to the Wisconsin Department of Justice. The DOJ, in turn, sent the file to the Waukesha County Sheriff’s Office. A sheriff’s investigator opened the video and confirmed it contained CSAM. Detectives traced the account to Gasper and obtained a search warrant for his residence and devices. Officers later found additional illegal files on his phone. Gasper eventually admitted he had accessed the material.
“A private search does not become a government search simply because an officer confirms what the private party already found.”
The Fourth Amendment does not restrict private citizens. As long as the citizen is not acting at an officer’s invitation or direction, items viewed and seized by the citizen may be used as evidence even if they are located during a search that would have been unlawful if it had been conducted by an officer: “Whether a private party should be deemed an agent or instrument of the Government for Fourth Amendment purposes necessarily turns on the degree of the Government’s participation in the private party’s activities” (Skinner v. Railway Labor Executives’ Ass’n, 489 U.S. 602 (1989)).
But this case turned on the Fourth Amendment principle of private searches. Did officers conduct an unlawful search when they watched the video without first obtaining a warrant? Gasper argued they did. His position was simple: The fire had been flagged by Snapchat’s automated software. No human had actually viewed it. According to the defense, that meant the government’s viewing of the video was a new search, not a repetition of a private one. The trial court agreed and suppressed the evidence.
The Wisconsin Supreme Court reversed. The court relied on the private-search doctrine, a rule the U.S. Supreme Court established in United States v. Jacobsen. The Fourth Amendment limits government searches — but not private ones. When a private party searches something and exposes evidence to police, officers may examine the same material so long as they do not exceed the scope of the private search. A private search does not become a government search simply because an officer confirms what the private party already found.
Snapchat’s technology had already analyzed the contents of the file. PhotoDNA does not merely look at filenames or metadata. It analyzes the digital structure of the image or video and compares it against known CSAM files. When Snapchat flagged the video, the system had effectively determined the file matched previously identified CSAM. Because of that, the court said officers had “virtual certainty” about what the file contained. Watching the video did not reveal anything meaningfully different from what Snapchat’s scan had already established. The officer’s viewing therefore did not exceed the scope of the private search. No Fourth Amendment search occurred.
Gasper argued the private-search doctrine should only apply if a human being conducted the original search. The court rejected that argument. Nothing in the doctrine requires human eyes. What matters is what the private search revealed — not how it was conducted. Snapchat had already identified the file as CSAM. The officer simply confirmed it.
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Practical takeaways for officers:
- Technology companies increasingly conduct the first search. Platforms such as Snapchat, Google, and Dropbox routinely scan uploaded files for known illegal images. When those systems flag content and report it, that detection is treated as a private search.
- Officers may generally examine what the private party (including the private computer platform) already found. When a CyberTip identifies a specific file, reviewing that file usually does not violate the Fourth Amendment if officers stay within the scope of the private search.
- Scope still matters. Opening additional files or exploring an entire account could raise different constitutional issues. The private-search doctrine only covers what the private party already examined.
- Though the search was allowed in this case, many courts disagree (see our discussion of United States v. Lowers). The wisest course of action is to obtain a search warrant before an officer views a file identified as contraband by a computer program.
Hash matching generates powerful evidence. Courts increasingly treat hash values as a digital fingerprint. When file’s hash matches the hash value of a known CSAM file, that match can strongly support probable cause for search warrants.
Criminal investigations increasingly begin with automated detection systems rather than street encounters. Technology companies scan, flag, and report illegal material before law enforcement even knows the evidence exists. The Fourth Amendment still applies, but when a private actor has already identified contraband and turned it over to law enforcement, the Constitution does not require officers to ignore it.
Bottom line: The law does not require police to avert their eyes from evidence that a private party has already uncovered.
Note: Courts remain divided on whether a hash match alone constitutes a private search under the Fourth Amendment. As discussed in “CSAM and Hash Matching Tech: Tool for Catching Creeps,” some courts treat hash-matching as functionally revealing contraband with near certainty, while others conclude opening a file still exposes new information beyond the scope of any prior private search, creating an ongoing split in how these cases are analyzed. It’s important to know what rules are being applied in your own jurisdiction.
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