Tainted Blood (1993)

When little girls grow up, what will they be?

After a 17-year-old shoots his parents dead and then turns the gun on himself, an investigative reporter makes a disturbing discovery. The adopted boy was born to a mother who, as a teen, inexplicably murdered her parents as well. Even more alarming is the discovery that the dead boy has a twin, who may also be genetically predisposed to kill.