Virgil Incanto
Virgil Incanto was a serial killer with an unusual condition. He had a deficiency that meant he could not produce essential fatty acids. In order to counteract this lacking he would regurgitate a digestive juice that would break down the fat in his victims flesh and he would ingest it before the rest of the body dissolved. Mulder and Scully were called in to investigate the killings because of their bizarre nature.

Incanto chose his victims in internet chat rooms where larger women would go, using the alias 2Shy. Since they had more fat on their bodies than average, they were the perfect choice to feed his need. He was shot by one of his victims after he attacked Scully and attempted to digest her. He survived the gun shot and was in bad shape during his interrogation with Scully concerning the cases of 47 missing women. He was proud of the fact that they were all his victims and he showed no remorse for what he did to keep himself alive. It is presumable that he died of the condition later.