The memory of this encounter would come back to haunt him when his team traveled to M1B-129, to investigate an anomalous energy reading picked up by the MALP. There, after his team had discovered the bodies of several dead Genii and a cave containing a mysterious Wraith device, he began to experience paranoid flashbacks to his encounter with the super-soldiers. These eventually became so intense that Leonard mistook his own team members for enemy soldiers, hunting down and killing them all.
Leonard remained on the planet, continuing to believe himself threatened by attackers. The Dial Home Device had been sabotaged to explode as soon as someone was to dial it, probably by Leonard; he then lay in wait until Lt. Colonel John Sheppard arrived with a search party. Leonard ambushed the group after they had found his team and attempted to return to Atlantis, shooting Sgt. Barroso before falling back. He and Ronon Dex (who believed Leonard to be a Wraith) then hunted each other through the woods, with Leonard shooting and injuring Teyla Emmagan when she and Sheppard attempted to reach him.
Although he managed to evade Ronon, Leonard's delusions reached the point where he began firing blindly all around him, expending what remained of his ammunition. When Sheppard then approached him, Leonard still only saw himself as surrounded by super-soldiers; after radioing for backup, he chose to commit suicide by holding one of his Fragmentation grenades to his chest. (SGA: "Phantoms")