VIDEO: KGUN9 has learned a possible explanation for the trench collapse that killed a contractor and sent a Tucson Firefighter to the hospital. The accident happened in a parking lot on Stone just south of River. Workers were trenching to lay pipe. Now an unofficial explanation for the accident has emerged. A man close to the family of the victim tells us no one was in the trench when it collapsed. He says the contractor who was killed was standing on the surface when the ground collapsed and threw him into the crater that opened when the ground gave way. Simply looking at the mound of sand it looks soft. On the edge of the work area there's part of a protective wall used to shore up a trench and protect workers from a collapse.