I remember watching a video about this the day when he was shot. The gist of it:
- He had recently started criticizing Israel.
- he also refused money from Netanyahu.
- As soon as he was killed, Netanyahu started going all over American TV right away saying "it wasn't us".
- Israel pretty much immediately painted a mural of Kirk to claim him as a friend.
- Killing him allows them to put an Israel puppet in his place, while setting up that anti-Israel groyper guy as a scapegoat.
I don't care much for American celebrities, so I don't know whether any of this is true, but that was the "evidence" for Israel doing it.
There's a digital archive of his publications in Spanish: https://archivomagon.net/