Kritschgau went to a FBI lab to steal a core sample. He was interrupted by Dana Scully, but was able to duck out without alarm. She tried to detain him, but he pushed her down stairs to escape. His print was found at the scene and so Scully tried to arrest him at his work. After getting him at gunpoint, he told her arresting him would be useless, and that he would be killed. Further, he mentioned her cancer and told her there was a connection between those that gave her the cancer and the ones who would kill him.
Kritschgau waited for her to get Mulder back to his apartment in order to tell him the truth as he understood it. He explained that the entire alien and UFO conspiracy was nothing more than an elaborate series of lies to draw attention away from sinister military experiments on an unsuspecting public. So-called "abductions" were actually careful military tests involving chemical and biological warfare, among other things. Kritschgau's son died as a result of Gulf War Syndrome, which he felt party to because of his work at the Defense Advanced Research Projects Agency and connections to a pharmaceutical company called Roush Technologies. (TXF: "Gethsemane")
Kritschgau later called Mulder to tell him someone was listening in on him, Mulder hung up and killed the spy. Soon, he found Mulder at the DoD, having gotten in with Scott Ostlehoff's ID and took him aside, faking a laugh nervously in public. In his office, he told Mulder he could find out much more information with Ostlehoff's ID than just about Scully. As he walked Mulder to the level-4 security entrance, he described much of the military's actions over the past 50 years to deceive the public. (TXF: "Redux")
Following the incidents, Kritschgau was fired. He still believed his explanation for the conspiracy to be the truth, whereas ironically it was not. He testified as much during an FBI investigation into the death of Ostlehoff led by Scott Blevins and the Third Man. He said he did not know who killed Ostlehoff. He also said he had funding source from Roush Technologies, a congressional lobbying firm. (TXF: "Redux II")
In 1999, the discovery of an alien spacecraft off the coast of Africa caused Mulder to begin experiencing intense mental trauma. While in the hospital, Mulder requested that Skinner bring in Kritschgau, who would know what to do. Kritschgau recognized Mulder's symptoms from his work in the CIA and was able to identify the correct drug to slow down Mulder's brain activity to a normal level. He tried to help get Mulder out of the hospital, but was captured. (TXF: "The Sixth Extinction")
Kritschgau knew that Mulder was now proof of alien DNA and visited Scully in Mulder's office to insist that she let Mulder prove it rather than figuring out how to cure him. He even threatened to harm her if she did not. In secret, he had hacked into Scully's computer and taken the alien images, wanting to have them analyzed by the NIH. Unbeknownst to him, Scully was given a key book with Navajo writing and figured he had given it to her. She then came to his apartment and found he had hacked into her computer. Kritschgau challenged her for hiding the truth. His activity was unfortunately noticed by Alex Krycek, who then went to eliminate him and the files he took. (TXF: "The Sixth Extinction II: Amor Fati")
- "Gethsemane" (First appearance)
- "Redux II"
- "The Sixth Extinction"
- "The Sixth Extinction II: Amor Fati"