I hope that people aren't really taking this too seriously as a reason to suspect Israel. There was a LOT of chatter saying that they killed him, by the Nazis of course. A dominant narrative on /pol/ is basically that Kirk got in bed with the Jews and now he's paid the price for trusting them.
From the standpoint of your average left-leaning person, Israel making a statement like this seems completely out of the blue and makes them look really guilty. But there's a whole demographic of people who really think that they did it. I don't think it's too unreasonable that they would make a statement about it. And let me be clear. I absolutely hate Israel with all my heart. But there are plenty of events in this world that they are not responsible for.
More importantly, this seems dangerously close to reasoning like: "You wouldn't defend yourself against these accusations unless they were actually true!" Which is definitely not a good bar to set.