Luigi Mangione

Ghost guns still are usually made with parts from major manufacturers -barrels, slides, part of the receiver (see wired article).

Its impossible to track down the gun but if he was carrying it then its already tracked down. If he'd thrown it in a river it would hace been impossible for law enforcement to connect it to him unless they had video of him tossing it.

Since there's video of the gun at the crime (and it exhibits a very obvious design flaw) and he had it on him the rarity of such a gun will likely serve the opposite effect at trial.

https://www.wired.com/story/luigi-mangione-ghost-gun-built-tested/