Brown seems to be covering up for Mustapha and the police are going along with it. Looking at his picture, he does look like the pictures of the shooter posted on the internet. Brown scrubbed him from the website because they ended their association with him, for whatever reason. It wouldn't be a far reach to say he could be the person they're looking for.

They haven't denied it so its possible. Mustapha looks like the Allahu Akbar type.