Butch Cassidy and the Sundance Kid are arguably America's most memorable outlaws, but a lot of contention continues to exist over what happened to them later in their lives.

Butch Cassidy, whose real name is Robert Leroy Parker, and the Sundance Kid, Harry Alonzo Longabaugh, led a notorious gang of armed robbers and cattle rustlers, known as the Wild Bunch, who raided and caused havoc in many part of the American West in the 19th century.

Although both Butch Cassidy and the Sundance Kid reportedly joined the Wild Bunch in the late 80s, both men rose to prominence as the most charismatic members of the robbers.

The headline-grabbing exploits of Butch Cassidy and his gang were much to the dislike of the authorities, who went to great ends to capture the bandits. The Wild Bunch are believed to have operated in New Mexico, Wyoming, South Dakota and Nevada. Historians say the group stole tens of thousands of dollars during their raids, which often targeted trains and banks.

Eventually, being in the American West became too dangerous for the group, so Butch Cassidy and Sundance Kid headed to South America. It is there that after trying out life as rural farmers, they are said to have met their deaths when they turned to robbery in the foreign land.

But there have been rumors over the years that both men never died but returned to the American West and lived out their lives quietly. The case of the Sundance Kid has been the most compelling in this regard.

For many years, a Utah man known as William Henry Long was linked with the Sundance Kid. Both men, who have a striking resemblance, also have ties to the notorious Wild Bunch.

A book by author and researcher Marilyn Grace, which was released in Dec. 2014, seeks to trace the ties between Sundance and Long. The book, Finding Butch Cassidy and the Sundance Kid, is the result of nearly two decades of research.

Grace argues that Sundance changed his name to William Henry Long and resettled in Utah in 1894, where he married Luzernia Allred Morrell, who had six children. "It's a great cover, to be married with six children instead of an outlaw on the loose," Grace notes.

But after testing samples of DNA from the exhumed body of Long and a relative of Sundance in 2009, investigators were forced to come up with a way to support their theory of the survival of the outlaw without genetic evidence. The researchers said it is possible that the samples had somehow been contaminated with others. Also, there were suggestions that Sundance may have been adopted into the Longabauch family.

Whatever the case, there are obvious things connecting both men. According to Grace, both Long and Sundance had broken noses, as well as a notch in the ear and the chin. Although records are sparse, both men are reportedly listed to have been born by a woman by the same name 'Ann' in their papers.

What do you think? Could America's greatest outlaws have outsmarted the law and even our history books.