Yeah. Show me ONE.
Anyone with the skill and motivation to build one of these, is not likely to go through all that trouble to use it in a crime, when one can just steal a gun with a lot less effort.
There is no paper trail if the weapon is stolen or purchased on the black market.
Unfortunately, there was at least one.
https://www.ammoland.com/2015/08/ghost-gun-used-in-murder-suicide/#axzz4zNdp0yvT