Immunity in exchange for testimony
<p>Suppose John Doe is on trial for murder and Jane Smith is called as a witness. Suppose some question prompts Jane to take the fifth against self incrimination. My understanding is that the prosecution can offer blanket immunity to Jane.</p>

<p>What happens if the prosecution offers blanket immunity to Jane, and then Jane admits to the murder and describes how she framed John? Is she free from prosecution for the crime of murder? Or can she only be immunized against other crimes, not the crimes that John has been charged with?</p>

<p>When you say "blanket immunity," I assume you're talking about <em>transactional</em> immunity -- the witness cannot ever be prosecuted for any crimes they testified about. This immunity is actually broader than that required by the US Constitution (although some states do require it). However, if it's provided, it absolutely covers crimes connected to what John is accused of. One very common use of immunity is to give a co-conspirator immunity to testify against another co-conspirator being charged with conspiracy. If transactional immunity wouldn't cover that conspiracy charge, it would pretty much defeat the purpose.</p>

criminal-law witnesses