In February, Caleb McGillvary used a hatchet to break up an assault and his interview with a TV station made him a star.
He was arrested in Philadelphia, accused of killing 73-year-old Joseph Galfy.
Police say Galfy drove to New York City to pick Kai up last Saturday, and then spent the weekend at Galfy’s home.
Police believe the two may have had a sexual encounter.
McGillvary’s last Facebook posting said he was drugged and raped, and asked, “What would you have done?”