If you're going to kill someone close up, it requires you to participate. If you're far enough away though, you don't even have to know it happened
If you sitting in a cockpit at 20,000 feet and you push a button that opens the bomb bay and releases a string of 500 pound bombs, you are not engaged, you're just part of a system. Someone else decided, the aircraft and the payload was provided, you're removed from the decision and as much as possible, from the consequences.
Make a robot to fly the plane and release the bombs, and even that minimal responsibility is gone, now it is all death by committee and programming. Give that robot the right programming and no one even has to know what happens.
This time it was a pound of C4 attached to a bomb squad robot.
A man, very likely guilty of murder, but a man nonetheless, was executed by police using C4 and remote control. They could have waited, he was not in a position to be any further threat, they had him isolated and pinned down, but they chose to act.
It's not a slippery slope as some pundits have suggested. It's a cliff.