Different types of footwear leave different impressions in the soil. If foot prints are noted at a crime scene and if investigators have been trained in the procedure impressions can be made. The procedure is fairly simple using plaster of paris. Water is mixed with the powder of the plaster and a mud is made. The mud is then simply poured slowly over the foot print in the dirt, sand, or snow. It is allowed time to dry, usually about thirty minutes, then the cast is simply picked up and admitted into evidence. This type of evidence can be valuable in either ruling out or ruling in a suspect. The cast is measured to ascertain the size of the imprint/shoe and one can tell the type of shoe/boot etc. from the impression left at the scene.