It's not hard to detect who you were killed by if your bow and bomb (unless you use putbomb) have custom scripts for compatibility with gmaps.
I'd imagine if you had a function to find the closest player with the sword animation within range when you the player dies, that would pretty much pinpoint the killer, but it's not a perfect detection method and could produce false positives.
I.e:
PHP Code:
//#CLIENTSIDE
function onPlayerDies() {
// Find closest player with sword animation
// Other Script..
}