Use the Microscope: Pink Fibers > Pink Bra. Then the Trace Analysis Computer: Fingerprints from Laptop Case > Ed's Fingerprints. Now head to Brass’ office and ask everything before getting a warrant for Anthony and Billy. Quiz them and then do the same with Keith.
I'm playing this game right now and I get stuck once during the first case. Just trying to contribute, it might help. If you get stuck: