In a military sexual assault prosecution, the investigation usually focuses on one person early. Once that focus sets in, leads pointing to a different perpetrator can go unexamined. When the defense later argues that someone else committed the offense, the strength of that argument often depends on whether investigators pursued or ignored evidence of an alternate suspect. Whether a failure to investigate alternate suspects rises to a due process violation depends on a careful distinction between what the government suppressed and what it simply never collected.
The constitutional baseline
The Due Process Clause guarantees an accused a fair trial, and a central component of that guarantee is the prosecution’s duty to disclose favorable evidence. Under Brady v. Maryland, 373 U.S. 83 (1963), the government must turn over evidence favorable to the accused that is material to guilt or punishment, including evidence that points toward a different suspect. Courts have recognized that evidence of an alternate suspect can be powerful Brady material, because in the hands of the defense it can support an alternative theory of the crime and can be used to discredit the thoroughness of the investigation.
These principles apply in courts-martial. The military discovery rules, including Rule for Courts-Martial 701, reinforce the constitutional duty by requiring trial counsel to disclose evidence favorable to the defense. So if investigators developed information about another possible perpetrator and the government withheld it, that is a classic due process problem, and the materiality standard governs the remedy: relief is warranted where there is a reasonable probability that disclosure would have changed the result.
Suppression versus failure to develop
The harder question is what happens when the alternate-suspect evidence was never gathered at all. There is an important difference between suppressing favorable evidence that exists in the government’s files and failing to investigate a lead that might have produced such evidence. The Brady duty attaches to evidence the government possesses or controls. It does not, by its own terms, require the police or investigators to chase down every conceivable lead.
This means a bare failure to investigate alternate suspects is not automatically a Brady violation. The constitutional violation is most clearly established when the government had favorable information about another suspect and did not disclose it. When investigators simply declined to pursue a lead, the defense must usually frame the problem differently.
How the defense uses an inadequate investigation
Even where a failure …