A team of retired investigators, Kevin Gannon, Anthony Duarte, Mike Donovan and Dr. Lee Gilbertson, say a spray-painted smiley face could be the disturbing signature of a nationwide network of serial killers who target college-aged men.

The chilling symbol has been seen near many of the sites where these young men have been found in incidents that police ruled accidental drownings. But Oxygen’s new six-part true crime docuseries, Smiley Face Killers: The Hunt for Justice, follows six mothers who are in disbelief that this tragedy has happened to their family. Could the drowning deaths of these young men be the work of a group of serial killers who are still on the loose?

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