[Justa]

Ok, so the perp will break the law and kill a federal attorney but he'll comply with a request by the FBI to turn in the barrell?

Reason check = Fail.

[Bogey78O]

No it's perfectly reasoned.

Only the killer will refuse. So whoever refuses has to be a criminal.

[Kenny Bunk]

You two are having a problem mastering FLEL-THINK (Federal Law Enforcement Logic). Let me walk you through this pari passu

Sophisticated scientific mumbojammery which no one outside the government could possibly understand, indicates that the vic was shot by the perp using a Makarov with a Fedarmco barrel. No doubt about it.
Now by getting every available Mak barrel made by Fedarmco, and using the same mumbojammery to "fingerprint" them, our government servants will build a database of those who did NOT do it. Since, brilliant forensic psycho-warriors that they are, they know that the perp is unlikely to turn his Mak Fedarmco replacement barrel in, all they have to do is interrogate everyone else. What don't you get?

They will then carefully eliminate innocent suspects until the crazed caucasian militia-fanatic lone gunman is isolated by this process of elimination and drives his white van with the ladder on the roof rack to the Smokies, where he will be surrounded in a cave by ATF agents.

I had feared that when PC Moose, Ph.D, resigned to pursue literature, this sort of straight-forward logical law-enforcement would be lost to us. Not so. Moose lives on in spirit in the world of FLEL-THINK!