(Reuters) – A Florida teen was detained in western New York after he tried to cross the U.S.-Canada border late on Friday, as police sought to question him after they discovered what they believe is the body of his grandmother, U.S. border patrol agents said on Saturday.

Logan Mott of Neptune Beach, Florida, was held in Buffalo after he drove on to a bridge leading to Canada and then apparently turned back toward the U.S. side, where he encountered border agents, officials said.

Officers discovered Mott was wanted on a warrant for auto theft and was a person of interest in a death investigation, U.S. Border Patrol Officer Aaron Bowker said Saturday.

Mott, 15, and his grandmother, Kristina French, 53, were initially thought to be missing earlier in the week when they failed to pick up Mott’s father at the airport, according to the Jacksonville Sheriff’s Office and local media.

Mott’s home had been ransacked and some weapons were missing, as was his grandmother’s vehicle.

On Thursday, police found remains in a grave they said they believed to be that of French, the Jacksonville Sheriff’s Office said on Twitter. The office could not be reached on Saturday.

Mott was being held by the Buffalo Police Department on the auto theft charge, the border patrol said.