It sounds like they are changing the story, to fit their narrative. The original description of what happened, didn't sound like the way Israel handles assassinations. It sounded more like the sort of way other intelligence services, might aid and provoke a more directly involved militant group, to carry out a larger scale attack than they are usually able.
This would make sense if say, the CIA wanted to poke Iran, to provoke them, while also setting back their programs. Just equip and supply to help the Mujaheddin carry out a larger attack, deeper in Iran, to a more critical target than they would normally be able to reach.
Iran would then bluster and make excuses to try to blame Israel, while they would most likely retaliate against America anyway, because "The Great Satan" is a more rewarding target than "The Little Satan".
Thus providing the US Military-Industrial Complex with its required rival.
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