How do you know? A could be mentally ill, and thus innocent. A could be an undercover officer, or shooting in self defence against a threat you didn't see. And so on.<p>You can say "in my opinion, A is a murderer" -- but the only time you should be making a statement of fact on A's guilt is <i>after</i> it has been proven beyond a reasonable doubt.<p>To do otherwise is to dishonestly masquerade your opinion as fact and to expose yourself to a nice fat libel lawsuit along the way.