It depends on where you are, and what gangs have formed there, and what kind of microculture they happen to have developed.

In Barcelona, it may be Moroccans as you say.

Here in my city the crime is perpetrated mostly by a small number of recidivist Maori and a small number of recidivist NZ Europeans, as well as by youth, and I haven't heard of any crimes from the Syrian immigrants (who all profess to be Muslim) as far as I can recall.  So my point is that being Muslim isn't coorelated with criminal activity in general... even if it might happen to be true in certain parts of Europe for one reason or another.  And therefore arguments against Islam that are based on that culture being incompatible with Western culture don't hold as much weight in my mind as they used to (although it still has some weight) because I see a counterexample right in front of me.