The Atlantis expedition told them that they were suffering from a plague that caused memory loss, but Lathan didn't trust them. Talking to some of the others, he urged them to try to overpower the soldiers there and try to hijack the ship in orbit, but Michael Kenmore, who had been similarly affected, said that the plague threat was too great, and the others agreed.
Believing that he was right, Lathan skipped a treatment. While off the retrovirus, memories began to return, and he told this to Michael. Michael, who was part of a group who already knew something was wrong, decided that Lathan was too great a risk. They killed Lathan by snapping his neck and dump his body making it look like his death was due to an accident. (SGA: "No Man's Land", "Misbegotten")