If you had a drone with a weapon, I would think you'd want to fire on someone using some variation of Tracking Point style hardware [1], except partially self aimed. Basically see the target, paint the target, drone uses internal sensors to detect a brief instant of random stability and fires the weapon

http://arstechnica.com/gadgets/2014/08/gun-linux-on-the-rang...

Again, doing a crime and getting away with a crime are two enormously different things. The truth is that the majority of humanity can commit terrible crimes with utter ease. There is absolutely no question about that.

Most of us don't, however, because of morality and our nature. The rest don't because they don't want to spend the rest of their life in jail, and for major crimes the probability of getting caught is enormously high. Things that reduce that probability (and a device that means you don't have to be on or even near the site, and can extract 100% of evidence with a very high degree of success, does that) open up opportunities for people to do such crimes.

As a parallel, someone mentioned bitcoins, and bitcoins absolutely opened up the world of casual extortion, because suddenly you don't have to go to a mailbox or meet in a park.

I'm not a detective, but I suspect having the large, complex piece of electronic equipment that was used as the weapon would be a godsend compared to the evidence available in a normal murder or assassination investigation.