The X-Files: Eve is a novella written by Ellen Steiber. It was first published in 1997.
Description[]
When two grisly identical murders happen simultaneously on different coasts, Mulder and Scully have only one clue: two identical girls who may or, may not be criminally involved. Their investigation leads them to a DNA-splicing doctor and a terrifying question: Were these little girls created as killing machines?
Mulder and Scully need to find out before the next crop of killers is born...