[PrivatioBoni]

I meant I changed it to what you had on your code before.

For reference, in this case:

killerid = the person who made the kill which caused the callback to be called
playerid = the victim

For the score, you got the score of the victim and gave it to the killer and added 10.
Also, you sent a message to the victim saying they killed someone, which is wrong.

Try it and see if it works better, including the killerid != INVALID_PLAYER_ID code (which checks if the killer is a valid player).