Investigation Discovery's EVIL TWINS Premieres Tonight, 7/26

There's something inherently fascinating about twins. Maybe it's the secret languages they create, their identical facade, or the theory that one can feel when the other is hurt. But when one twin turns toxic, does the other stay pure of heart? Channeling sibling rivalries and deadly childhood pacts, EVIL TWINS follows true-crime mysteries surrounding cases of these double-duty archetypes. Each episode reveals a pair of sinister siblings: twins who tag team to kill together, twins who turn on each other, and even the good twin versus the evil. Taking two timing to a whole new level, the three-part series EVIL TWINS premieres tonight, July 26 at 10 PM E/P on Investigation Discovery.

"Deadly duos are something we profile often on Investigation Discovery, but when you add in the lure of two people who share the same genes committing dark deeds, separately or together, there is an added element of intrigue," said Henry Schleiff, president and general manager, Investigation Discovery. "When the only thing that makes you one of a kind is that you're one of a pair, EVIL TWINS features extreme stories of DNA-sharing siblings that snap."

Attempting to tackle the nature vs. nurture debate, EVIL TWINS explores the belief that psychopathic behavior may be preprogrammed. With tales of twins living apart yet sharing identical criminal records, twins teaming up to murder, and cases in which only one twin turned twisted, stories profiled in the premiere season include:

A Tale of Two Sisters Premieres tonight, July 26 at 10 PM Sometimes your mirror image can become a horrifying sight. Identical twins Sunny and Jeena Han left South Korea to live in California at the age of 12, and the stresses of living in a foreign city only strengthened their bond. But as the pressures of high school weighed on them, the Han sisters became bitterly competitive for grades, love, and attention. Even though they lived apart during college, they separately descended into a world of addiction, theft, and prison. The sisters' long history as rivals would erupt into a bloody battle, pushing one to order a hit on her other half. Once best friends, the Han sisters eventually found themselves on opposite sides of the courtroom. Location: Orange County, CA

Bad Seeds Premieres Thursday, August 2 at 10 PM Overly competitive from the start, Robert and Stephen Spahalski were considered two parts of an evil whole. As teenagers, the two used their superlative athletic abilities to commit petty crimes in order to finance their escalating drug habits. When a murder put Stephen in jail, Robert went on to lead a life of crime alone. Leaving at least four bodies in his wake, Robert solidified himself as a dangerous serial killer and eventually turned himself into the police to join his brother behind bars. Featuring an extensive prison interview with Robert, the violent journey of these brothers from simply identical twins to disturbingly identical killers raises difficult questions about the very nature of evil itself: is it born or is it made? Location: Rochester, NY