Killing a homeless person should be safe if you use a good method of killing and have a plan
But they often shift around, so it'd be difficult to plan on an exact spot. And most importantly, I'd want some level of credit for the deed, just as Jack the Ripper.
I'm not Ted Bundy or anything, but I could plan on killing someone and get away with it. It's just that I don't have that sense of purpose and daring, because that feeling often comes and goes in spurts. I can hurt someone if they really provoke me though, but so can most normal people.
I've been in situations where I've drawn, but they were defused by the opposing party. That brought me some mild euphoria.
I could just offer some homeless bum drink that's been poisoned and get away with it.. But that wouldn't bring about any sense of accomplishment or anything.