i don't know if he can be retried for murder one, but there's a whole host of other charges that could be brought, depending on the statutes of limitations attached to them, like tampering with/concealing evidence, perjury, second-degree murder (manslaughter, et al), if he was only charged with and acquitted of first degree murder, etc. They might not be able to nail him for murder one because of double jeopardy, but that doesn't mean that he walks away fancy-free.When the knife was found, the trial was over. Is it still evidence when the trial is over? Once someone is acquitted, the case can't be reopened. So I'm not sure that the policeman did anything illegal. If the knife does turn out to be a murder weapon, it will be interesting to see what the legal ramifications are for the policeman that kept the knife.
But until or unless DNA proves that it's THE murder weapon, I call bullhockey.