David McNamara was the head of security for Cedar Mills Psychiatric Hospital and responsible for redesigning the security in lieu of Ackerman's arrival. He was formerly a soldier deployed in Iraq and suffers from panic attacks and flashbacks. He leads the manhunt through the prison for Ackerman, directing them to the basement. He is struck in the shoulder with a hammer and then stabbed with a screwdriver before Ackerman captures him.
McNamara is tied to a chair and made to watch as his lover Jennifer Kelly decides to pull a switch on the wall to electrocute both him and Ackerman. The switch was a test devised by Ackerman, and McNamara realizes just how far Kelly would go for her revenge.
In The Cage, McNamara is finalizing his divorce to his ex-wife, who cheated on him while he was serving in Iraq. He also apparently had a drug problem prior to deployment.
He carries around his mother's wedding ring in his pocket (he inherited it when he was seventeen and she passed away). He considers proposing to Jennifer Kelly within six months with the ring, after she meets his daughter.