Since 1997, hundreds of athletic, affluent, college-aged men have reportedly been found dead in bodies of water from New York to Minnesota. Although nearly all of the cases have been classified as accidental or undetermined drownings, a team of retired NYPD detectives have a theory that at least 40 of these victims were killed by an organized underground gang referred to as the “Smiley Face Killers” -- named for graffiti of a smiley face allegedly found near many of the bodies.

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Mothers of six of the young men -- Dakota, Will, Luke, Todd, Tommy and Brian -- say there is no way that their healthy sons would have accidentally tripped and fallen into a body of water and drowned; they say they believe their sons were murdered.

The moms share why they believe their sons did not die accidentally, in the video above. Plus, hear what these women say they were told by police about how their sons died.

WATCH: 'I Do Not Want This To Happen To One More Mother,' Says Woman Who Believes Her Son Was Murdered

On Wednesday’s episode of Dr. Phil, the team of detectives who have been investigating the "Smiley Face Killers" theory for the past 12 years share some of their findings. Could the deaths of these young men be the work of a group of serial killers who are still on the loose? Check here to find out where you can watch.

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Why A Retired NYPD Detective Says He Believes A Group Of Serial Killers Is Targeting College-Aged Men