I believe the only two murders that used Title II weapons (Class 3 is the type of dealer license, not the designation for the firearm) were both police officers. One used a weapon purchased by the department and the other personally owned his.
But, yeah, there's been two instances.
On the flip side I also know of two instances where Title II stuff was used legally. I think both can be found by searching Ayoob's blog archives. I know the latter one is in there.
The first was a Class 3 dealer using his Title II guns when he found a group of men breaking into his shop. His house was basically next door. They were there to steal machine guns, at least one of them died when he shot into the car. Or rather the perp died when his car crashed into a telephone pole after he'd been shot. Something along those lines.
The other, and this one is kinda funny in the "you's an idiot" area... guy is driving down the road with his wife or GF, ticked off somebody, said somebodies started shooting at them with .357 revolvers if not something else as they fled the area, guy drove to work because it was a secure place with a locked gate. When he arrived at his place of work, H&K, they had followed him through the gate. He reached into the back seat, grabbed a Ruger 556 (demo model, he was a Class 3 sales rep) loaded it up and shot 9 rounds into the ceiling of the parking garage as a warning. The dude that charged him's last words were "F*ck you and your machine gun."
Yep, no pity for that idiot.
