DALLAS — The family of a Texas teen who hanged himself says their son was involved in a ghoulish online game that calls on participants to complete a series of tasks before taking their own lives, and some schools are warning parents about the so-called Blue Whale Challenge.

Jorge Gonzalez told San Antonio television station WOAI that he wanted to caution others after his son, Isaiah, was found hanging in his bedroom closet Saturday in the family’s home with his cellphone propped up on a shoe to record his death.

A report on the boy’s death from the San Antonio Police Department does not mention the challenge. But Gonzalez’ family said in the days after the teen died, they pieced together from his social media and communication with friends that he had participated in the game.

His sister, Alexis, told the TV station that a person behind the challenge had gathered personal information from Isaiah and had threatened to harm the family.

The police department did not return a message left by The Associated Press asking whether authorities were investigating the game as a factor in the case. Many parents and other authorities are skeptical that the game actually exists, citing a lack of suicides directly attributed to it.

Agent Michelle Lee of the FBI’s San Antonio office said the agency is not assisting in the investigation, but urged parents to monitor their children’s online activities.