Well a university in New Zealand got the ok to blast pigs in the head with a Glock for a blood spatter study - https://www.rnz.co.nz/news/national/284438/how-did-shooting-...

I thought firing a gun would leave gunpowder residue on your hands

I'm pretty sure there are other ways of putting gun powder resedue on someone.

Yes, the point is that unless they actually take the time to do something like that, you might see that the victim has no residue on their hand and could not have shot themselves.

If you are an organ donor, it will surprise you what kind of research is done using corpses.

For example, "body farms".