Season 4 Episode 5 - Divide and Conquer

During a meeting with the Tok'ra high council, Major Graham of the SGC goes berserk, firing uncontrollably upon the Tok'ra before taking his own life. The SGC is stunned to discover that Graham is a Zatarc, the victim of Goa'uld mind control technology. According to Anise, its victims are subconsciously programmed to kill, their recollection of the procedure covered by false memories. Anyone who has come into contact with the Goa'uld could well be a Zatarc - and wholly unaware of the fact. Through the use of an experimental testing device designed by the Tok'ra, Anise sets out to determine who, at the SGC, has been programmed. The test proves successful in uncovering a second Zatarc - Lieutenant Astor, a former teammate of Graham's, who also goes berserk, shooting up the SGC before turning the gun on herself. But subsequent testing uncovers false memories in two more members of the SGC: Colonel Jack O'Neill and Major Samantha Carter.