[John Beresford Tipton]

"No, you can't be sued , arrested or pilloried in America for offering up opinions"

The key here is "opinions"
You are probably safe to say "In my opinion, X is a murderer."

You are in deep shit to say "X is a murderer" unless you are prepared to prove that X is in fact a murderer.

[dead]

You are in deep shit to say "X is a murderer" unless you are prepared to prove that X is in fact a murderer.

OJ is a murderer.

[Bikers4Bush]

So what do you call someone who is in the process of murdering someone? A committed murderer?

[jwalsh07]

You are in deep shit to say "X is a murderer" unless you are prepared to prove that X is in fact a murderer.

In your world pro lifers who believe that abortionists commit murder and say so are liable to defamation suits.

Welcome to the Rhineland.