Is there a way to detect which unit killed a unit? Preferably without EUDs.

in general cases: NO!
if you have only 1 unit per player: yes (killscore)

At least u can say that it was a unit inside the longest weapon range ingame around the killed unit (unit is in a location or location system on the killed unit).

Without EUDs? No. Kills are player based.
You could try and set up a system that detects death of a unit and then checks the units that are nearby. But that would be obviously very inaccurate.

With EUDs? Probably not. The only thing I can think of that is detectable is the kills counter going up when it killed a unit. Don't know if that is detectable via EUDs. If it is you had to combine it with deaths detection which has a percentage chance of failing.

It only goes up to 255 too, but it should be detectable, since it's a property of a unit.

well there is a way, but that pretty much depends on your map structure, i have a very complicated concept that might work yes without EUDS

If the player only has one unit it isnt hard to detect

or have a lot of units diff players with diff types of units