At this point, I think most anyone who doubts muslum involvement is biased in some way. There are tons of events involving terrorists where state agencies enable and fund a few extremists, under the guise of "building a case" against them. Then these individuals either slip away from surveillance, or are actively permitted to proceed with their plans.

This is the gray area of plausible deniability between "organic" terrorism and false flag events. In essence, an event like seen in Brussels could be both, or neither. The only people that can ever be held responsible are polocy makers, and they're largely immune to any consequences for their actions.