Marks were found on several abductees in 1992, with each abductee having two of the marks on their lower back.
Karen Swenson had the marks and a peculiar substance in the tissue surrounding them, when she died in Collum National Forest in March 1992. About the same time, other killed individuals who bore the marks included a person in Sturgis, South Dakota and another in Shamrock, Texas. Although three other members of Karen Swenson's high school class (including Ray Soames) had died in similarly unexplained circumstances, their autopsy reports – which had been signed by a different medical examiner than the one who signed an autopsy report on Karen Swenson – included no mention of the marks or anomalies in the surrounding tissue.
The marks were initially the only piece of remarkable evidence in the investigation of Karen Swenson's death. As such, they were shown by Coroner John Truitt to Detective Miles and by FBI Special Agent Fox Mulder to his newly assigned FBI partner, Agent Dana Scully. When asked by Mulder to identify the marks, Scully suggested that they could possibly be needle punctures, an animal bite or from electrocution of some kind. She knew immediately that the substance in the surrounding tissue was organic and, despite being at a loss for what else the substance was, she guessed that it was possibly a synthetic protein.
While investigating the deaths in Oregon, Mulder showed Scully that Peggy O'Dell, a patient at Oregon Memorial Psychiatric Hospital, also had the marks. Moments later, an irritated Scully asked Mulder how he knew that Peggy would have the marks but Scully did not believe him when he claimed that he had merely had a lucky guess. After he admitted that he believed the teens marked with the two spots had been abducted, Scully argued that the marks on Peggy O'Dell could have caused her to develop her pronounced psychosis.
Scully later worried, however, that bumps on her lower back were the same marks as the teenagers had, but Mulder determined that these spots were merely mosquito bites, to Scully's great relief. Theresa Nemman also feared for her own wellbeing, upon coming to the agents with news that she had the marks.
Soon thereafter, Mulder guesstimated that the marks were from some kind of test being done on the teens that might also be responsible for a form of genetic mutation, explaining the presence of a mammalian corpse in Ray Soames' coffin.
Billy Miles, who was also confined to Oregon Memorial Psychiatric Hospital – as he was experiencing a "waking coma" – also had the marks and, upon watching him hold Theresa Nemman up to an extremely bright light while leaves whirled around them, Mulder saw that Billy had the marks. The spots on both Theresa Nemman and Billy Miles' lower backs disappeared, however, once the light had dissipated. (TXF: "Pilot")