ELI5?
Unfortunately much like "rag with chloroform" or "killer with a black glove" became stock images in movies, "Gun with a silencer means a PROFESSIONAL KILLER" is a pure invention.
So the cops find a gun they can't trace, a dead body, no other physical evidence and frankly that sort of murder isn't typically solved.
take note, both styles require a team, this is not a solo venture if your in business you need cover and extraction, and supports, like a stage magician.
I am not a lawyer, but I am generally interested in firearms and firearms law.
A reasonably good source is Mark Smith on YouTube. He is an attorney.
Hope this helps.