They claim that the brothers were infiltrating Islamist terror network for US but went over to the other side.
Debka is universally thought to be the voice of the Mossad. I don’t know if that is true, but they wn’t do anything to jeopardize the relationship between Israel and America. That these brothers were spooks is abundantly clear at this point, what has happened in Boston is a very familiar narrative, but whether they went rogue is another matter.
Speculating based on other like false-flag events: They probably thought they were participating in a training exercise, which they probably had done before, and were sacrificed like the alleged London Tube Bombers and Lee Oswald