Little is known about McCarty's background, other than he served in the U.S. Marine Corps in some unspecified position, before joining the Des Plaines Police Department. McCarty also seemed to have some history of unprofessional behavior on the job, judging by his superior's lack of surprise when McCarty was considered a suspect.
McCarty is first seen watching the BAU give a profile on a sniper who is intentionally wounding his victims. When Hotch describes the unsub as a former or current member of the police department, McCarty gives him a snappy remark and is admonished by his commanding officer, Sergeant Weigart. As punishment for his remark, McCarty is assigned, by Weigart, to play the unsub during a reenactment of one of the shootings, which involved him having to be stuck in the trunk of a sedan all day. Frustrated by this, he leaks the profile to the press, despite the BAU's explicit instruction not to do so. Unbeknownst to him, the BAU also profiled the unsub as wanting to have contact with the media, in order to fuel his narcissism.
During the reenactment, JJ learns of the leak through a local news channel and has the reporter give her his source under threat of arrest, though he is only able to give a cellphone number. Garcia traces the number and identifies the cellphone as McCarty's. The BAU and local police realize that, because McCarty is playing as the unsub, he is armed, and become concerned that he might start shooting if he realizes something is wrong. As a result, they have a SWAT team covertly advance upon the sedan he is in, while the other actors remain calm and clear the area. Observing this, a confused McCarty tries contacting the others to know what is going on, but does not get a response because everyone silenced their radios. Moments later, the SWAT team tosses smoke grenades near his position, incapacitating him. Weigart then has him toss out his weapons and get out of the trunk slowly. Once he does, McCarty is arrested. However, as he is being hauled away, the unsub shoots him in the head from a distance, killing him instantly.