How have courts ruled on cached browser files as evidence of possession in CSAM prosecutions since 2015?
Executive summary
Since 2015 courts have produced a split and technical body of decisions about whether cached browser files (and similar cached/automated detections) constitute "possession" for CSAM prosecutions and whether government review of those files is constitutionally permissible; lower courts and circuits have oscillated between treating private provider scans as a valid “private search” that cures Fourth Amendment concerns and finding that government expansion of those scans or reliance on automated reports can violate the Fourth Amendment, with the Supreme Court yet to settle the issue [1] [2] [3].
1. The doctrinal frames courts use: “Present possession” vs. “evidence of” and the private-search doctrine
Two conceptual approaches dominate judicial and scholarly analysis: the Present Possession approach (does the cache place contraband under the defendant’s control now?) and the Evidence Of approach (does the cache merely point to other proof of possession), with scholars arguing the latter better captures technical realities of browser caches and transient files and affects how knowing possession is proved [4]; courts layer onto those evidentiary frameworks the private-search doctrine from Jacobsen, which asks whether a private actor (like Google or an email provider) performed the initial search and thereby insulated later government review from the Fourth Amendment [2] [5].
2. Circuit fractures: some appeals endorse private-search, others push back
Several federal circuits have concluded that when Internet content‐scanning tools (including hashing and automated flagging) are reliable and performed by private providers, subsequent government review can be treated as non‑governmental and thus lawful without a warrant, relying on high accuracy of hashing and analogies to Jacobsen [1] [5]; by contrast the Ninth Circuit in United States v. Wilson found that warrantless government viewing of files automatically reported by Google expanded the scope of the private search and thereby violated the Fourth Amendment on the record before it, highlighting factual gaps about whether what government agents viewed were exact duplicates of files previously inspected by a private employee [3] [2].
3. Cached browser files as a special technical problem for possession and authentication
Browser cache artifacts complicate possession inquiries because cached files may be transient, duplicated, or created by automated processes and not demonstrably under a user’s control; technical literature and prosecutors’ manuals stress different analytic routes — proving present possession through metadata and control versus treating caches as circumstantial evidence pointing to actual contraband on devices — and emphasize that forensic methodology and authentication under the Federal Rules of Evidence are decisive in admissibility [4] [6] [7].
4. The role of NCMEC, private reporting, AI flags and the state‑actor question
Congressional and CRS analyses report a further wrinkle: statutory reporting duties to NCMEC and automated AI flagging have produced inconsistent findings about whether reporting/processing by private actors rises to state action; some courts have suggested treating NCMEC or provider activity as state‑actor conduct in certain circumstances, potentially pulling otherwise private searches into Fourth Amendment scrutiny, while other circuits reject that transformation absent clearer government direction or control [1] [5] [8].
5. Practical litigation consequences and unresolved issues awaiting higher review
Practically, courts have not uniformly excluded evidence even when Fourth Amendment issues arose — some decisions invoke exceptions like the good‑faith or other doctrines, and district record quality (e.g., proof a private employee actually viewed duplicates) often decides suppression motions [1] [2] [3]; the net result since 2015 is a patchwork: cached browser files can and have been admitted as possession evidence in some jurisdictions where hashing, forensic linkage, or private‑search reasoning prevailed, but other courts have required warrants or found government review unconstitutional where the state effectively enlarged the private search or where automated tips were never human‑validated, and the Supreme Court has not definitively resolved the split [1] [2] [3].