Authorities believe Smithson strangled Shephard when he rejected his sexual advances.
Shephard had taken a semester off from Northern State University in Aberdeen, S.D., to work as an intern with Daktronics, a sports scoreboard manufacturer. The Cavalier, N.D., man was on a business trip to suburban Philadelphia when he was killed.
Smithson was the manager of Daktronic's local office. Police say he reported Shephard missing and told them he had dropped him off at his hotel the night before.
But investigators found Shephard's body in Smithson's basement.