Muslim women mostly wear black, long dresses. Why? I mean they could commit a crime and be on their merry way with it. Hell, men could wear them too if they aren't very tall and commit crimes. I don't get that. Please explain.
If Sister Alf2's explanation above is what you're alluding to, it could have been said better by you.
Are you talking about the face covering (niqab) as well? If so, the purpose of wearing these garments is not to commit a crime and I sincerely hope you refrain from attaching such a suspicion to them.
Muslims are commanded by God to be modest and to guard ourselves from immorality. For women, this can come in the form of concealing their bodies so as to conceal their sexuality. For most Muslim women, this means wearing clothing that conceals the entire body except the face and the hands. She does not have to cover like this in front of her husband, father and other male relatives.
However, there are some Muslim women that believe this means to cover the face as well as a woman's face can also add to her beauty. Therefore they believe in concealing that which can draw the unwanted attention of others.
It is a matter of maintaining modesty. I assure you they are not contemplating a life of crime when donning such garments.