I would think that another concern would be that he is "not a suspect... yet."
So say you draft him in the fourth round, and nothing is heard, everything seems okay... but no murderer has been found. So the police are still looking, and wouldn't you know it, in the middle of training camp they show up at the stadium with some silver bracelets for your guy. Because something finally cracked in the case. Or heck, maybe it happens in Week 3. Then what? You've lost a draft pick, the UFDA period is largely over, and you're back in the national spotlight for drafting a murderer. Bad press, bad mojo, major hole in the line... basically a worst-case scenario. Sure, there is always the best-case scenario too, but you can't think of one without the other.