Preston and his men searched the frozen tundra for escaped convict Ben Barker. Just as they were about to give up, one of Preston's men spotted a body. Barker was found lying dead in the snow. There were no tracks leading to or from the body. The cause of death was partially due to the unopened pack on his back. Barker did not die of thirst, hunger, or cold. What was in Barker's pack that led to his death?