The Iowa Fire Marshal is investigating the cause of a camper fire that claimed the lives of two elderly Minnesotans. The blaze broke out in a camper as the couple traveled along Interstate 380 near Waterloo Monday morning, headed for home. The victims are identified as Henry and Margorie Frank of Minneapolis — he was 82, she was 71. Their three pet dogs also died in the fire. When authorities arrived, the son and grandson of the victims were trying to get inside the burning camper, but the front doors were locked and the other doors were stuck. The preliminary investigation indicates an engine problem sparked the blaze.