No, you don't know that. Scum of the earth comes from all countries, the US and Israel included. FWIW, though, the most realistic scenario I can think of is that they may have had knowledge that something was going to happen, though maybe they didn't know the wheres and whens.
But, on the other hand, you can't discount the possibility that they did know exactly where and when.
Why can't some people even concede the possibility of Israeli terrorists? I don't have any idea how probable it is, but it's certainly possible. There are people in every single country on this earth who would kill their own mothers if it would further their own agendas.