was an odd catch. the tip must be submitted to law enforcement on or before september 30th. >> have you ever heard of an expiration date on a reward? >> i have not. >> south carolina son and mother who were gunned down -- >> reporter: it wasn't the only strange thing. on an interview on abc's "good morning america," murdoch's family member said their nephew, paul, had been getting threatening messages online before he was killed. >> i didn't think it was a credible threat. if it was, i would have tried to do something or notified someone. but i guess, you know, maybe i made a mistake. >> reporter: the family says the threat started after a fatal boating accident. >> paul, what >> 911, what is your emergency. >> we had a boat crash. >> february 2019, south carolina, paul murdoch and five friends all underage out