Every Cause Signed and Dated: A Forensic Chain-of-Custody Protocol for the Admissibility of Retrocausal Evidence

It is standard practice, in the laboratory and the courtroom alike, to throw out any evidence in which an effect is observed before its cause. We argue that this is a filing error, not a law of nature. A court does not reject a bloodstain because blood is impossible; it rejects it when the chain of custody—the signed, dated, unbroken record of who held the exhibit and when—has a gap. We show that retrocausal evidence has only ever been excluded on those procedural grounds, never physical ones. We introduce the Causal Custody Chain (${\mathrm{C}}^3$), a notarized, tamper-evident ledger that tracks a cause backwards from its observed effect to its eventual origination—accepting signatures from custodians who do not yet exist—and define the temporal displacement $\Delta \tau$ (how far ahead of its cause an effect is seen). Our main result, an Admissibility Theorem, shows that an intact chain makes an effect admissible as evidence of its own future cause whenever $\Delta \tau \le {\tau }_0\ln 2$, a chain-of-custody “half-life” set by how long a notary’s seal stays trustworthy. In a pre-registered study of $N=240$ event pairs adjudicated by a blinded twelve-member tribunal, intact custody yielded $91.3\%$ admissibility (rater agreement $\kappa =0.81$) and fixed ${\tau }_0=3.7\pm 0.2\mathrm{s}$. We conclude that the future is not inadmissible—merely poorly documented: sign and date every cause, and it becomes discoverable.