Matthew McCombs and Sean Brown were arrested last week as they tried to cross the border into Canada. Brown refused to waive extradition and remains in a Michigan jail, the Houston Chronicle reported.
McCombs was returned to Texas during the weekend.
Fort Bend County Sheriff William Wright said that McCombs admitted that he shot Ashton Glover, 16, of Sugar Land. He said that he and Brown invited Glover on a "mudding" trip -- driving across muddy fields.
Wright said that McCombs shot Glover in the head as the trio walked across a field. McCombs and Brown went to a restaurant to eat, returned to bury the body and then went home and slept.
Sue Smith, the victim's mother said she was "floored and speechless" after hearing the details, especially the alleged motive.