He was a physician assigned to Travis Marshall, on whom he wrote a psyche evaluation.
During the investigation of Santa Maria de Laredo, Dexter found two empty prescription bottles being used for paint thinner. One of them was for Chlorpromazine. It had been prescribed for Travis Marshall in 2006 by Dr. Carlson, a Miami doctor. Two refills were still left years later.
Detective Mike Anderson researched Dr. Carlson and the medicine. He found out that Carlson had died two years ago of unknown causes, but Mike did obtain his file on Travis. According to Carlson, Travis suffered from breaks from reality, violent tendencies since childhood, and lack of empathy. He was also a master manipulator and had delusions of grandeur. Carlson even believed that Travis was responsible for the deaths of both his parents, having grabbed the steering wheel to force their car into a tree killing them during his childhood. Carlson had prescribed Chlorpromazine for Travis. The medication is a form of anti-psychotic which helps decrease hallucinations.
Either the medicine was not effective or Travis did not take it properly, as he eventually killed a man named Professor James Gellar. Travis was under the belief that he and Gellar had been chosen by God to bring on the End of Days. Travis likely no longer took the medicine at all, thus causing his delusions as The Doomsday Killer.
- 2011 - Doomsday Tableaus are carried out by Travis
- 2009 - Dr. Carlson dies
- 2008 - Professor James Gellar is murdered by Travis
- 2006 - Dr. Carlson prescribes anti-psychotic med for Travis