A new paperback published by the St. Martin's True Crime Library addresses that question with definitive tales of a dozen sets of twins gone bad. The book is called 'Evil Twins: Chilling True Stories of Twins, Killing and Insanity' and its author, John Glatt, introduces readers in case after sad case of twins who either took their mysterious bonding to horrible extremes or in some instances, turned on each other.

If we excuse the sensationalistic manner in which the book was written, suspend disbelief as to whether we're reading completely factual accounts and overlook some glaring editorial mistakes (discrepancies in details, book typos, different spellings of first names) 'Evil Twins' does offer insight into some psychological examples of the closeness many twins share.

The stories tend to fall into three types: twins who entered a life of crime together and used each for support, twins who turned on each other with murderous consequences, or stories where one twin embarked on a crime and the other twin helped to cover up for his or her twin.

Some of the stories in the book are more well known (the infamous British Gangsters, the Kray Twins; June and Jennifer Gibbons who were known as The Silent Twins and had a British Opera written about their lives; Gina and Sunny Han, beautiful Korean-born twin sisters whose murder-for-hire tale resulted in a long prison sentence for Gina in California) while others will introduce you to twin brothers and sisters whose unhappy lives ended with tragic consequences.

Are there lessons we can draw from the stories? Perhaps. Many of the twins stories appear to be the results of horribly abused childhoods, and you would like to think that the love and support of a strong family upbringing would counter most societal pressures. Other stories in the book are obvious examples of twins with serious mental disorders that perhaps remained undiscovered or untreated despite signs that attention was needed.

And finally, in almost every chapter of the book, the love and bond between the two twins survives--even in unfortunate cases of where one twin kills the other. One particuarly haunting story is told of unseparable twin brothers Jeff and Greg Henry in which the more dominating brother Greg intimidated and ordered his slower brother Jeff around for almost all of their 35 years together.

After years of being controlled by Greg, Jeff snapped one night in 1991 and killed his twin with a shotgun blast to the chest. There are haunting photographs in the book of Greg's shocked look on his face he had as his brother murdered him as well as a stunned Jeff after the shooting, perhaps with the knowledge he would have to live the rest of his life knowing he killed the closest friend he ever had.

"He was my life," Greg told the book's author in 1998. "He was me. The only reason we fought was that I wasn't him. He would get angry at my weaknesses. He wanted me to be more like him." Proving that even evil twins carry a spot in their hearts for their twins.