Sometime during the day, Justin was captured by a crazed security officer and tied up and his head was covered with a sack. He was accused of looting the stores along with three other people. The three other captives were executed before Chuck arrived. Chuck tried to stop Seymour, but Justin was kicked off the scaffold and was killed as his body was hung.
Unlike Slappy, there is no head underneath Justin's sack over his head.
Justin's face is never seen in game, even in his notebook portrait he has a sack over his head and noose around his neck.
Those Seymour has already hanged were most likely his group of survivors as Justin screams "WE just needed food!".