No can do,
Either you would slay people who do it accidentally, or you would slay someone who did it on purpose. The risk of slaying innocent people is just to high, and as outsider you just can't keep track unles it's on the very start of a round, or you see it happen as an admin. It's stupid, and annoying, frustrating and it pisses people off yes. But in most cases the admins are powerless if it comes to shooting in melee, and what not with shooting teamkills.
Shamefully, but it's the fact. If we start slaying everyone, people will get pissed because they most likely didn't do it on purpose, or what not. And that's not something we want, the way it goes currently is the best we can do right now.