Clayton Maxwell

was the unsub in episode 3x05 "Closet Monster".

Maxwell was not a gamma. The Anomalous Crimes Task Force was sent after him because the Behavioral Analysis Unit could not figure out how someone could enter the houses of multiple victims without any trace:
 * Lau nodded. "Local PD are pretty sure they have a serial. And Down the Hall is pretty sure there's no way to circumvent that many locks and security systems. Which is why we're here."

As it turned out, Maxwell was a contractor working for local alarm companies.