I've never heard of one time use plastic suppressors, and them leaving traces behind, but I cannot claim it's never happened. I do know enough about them to say that a plastic suppressor is more likely to be a gun mounted grenade than anything else, which is why I think it's unlikely.
More likely is the killer trying to muffle the gun sound by sticking something over the muzzle, akin to the pillow over the gun you see on TV. In such an instance, there's not much chance of an illegal suppressor conviction. However, attempting to hide the gun sound is likely to show premeditation, which gets a murder 1 hit. But I am not a lawyer, that could be wrong.

I suspect that the National firearms act of 1934, which is the one that put suppressors, short barreled rifles and shotguns, machine guns, and other such items under control was, if not heavily, at least partly in response to the outlaw activity of the 20s, when gangsters seriously outgunned the police and fbi. At that time, the $200 tax was a very big sum of money, not affordable to most. It ended going into the local hardware store and buying a tommygun.

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