The large bones of the leg and arm are the most reliable for determining bone damage. The forensic investigator versed in burned bone analysis looks at both the macromorphology and the micromorphology of the fracture area. Perimortem, or pre death, fractures show up as relatively smooth breaks which continue uniformly through both wet bone and burned bone material. Due to extension and tension of the bone at the time of the break, these fractures will exhibit a pattern of microfractures, resulting in a typical butterfly pattern to the fracture. In contrast, postmortem fractures caused by the burning and drying out process exhibit fractures that are blocky and stepped in appearance. Human bone is composed of minerals, collagen and water. Water makes up 6% of bone by weight and 11% by volume. When the bone is burned, heat dehydrates the bone, driving out the water and destroying the collagen structure. Burning bones are subjected to heat induced expansion and shrinkage, and the existence of a thermal gradient, depending on the location of a specific bone in the resulting fire.
If a body has been dismembered before burning, the tool used (hatchet, saw, large knife, etc.) will leave a characteristic pattern of cut marks on the bones. Often there are several marks made by the same weapon, and these usually represent false starts made by the perpetrator in attempting to saw or cut through the bone. These marks often present as "W" or "V" shaped marks that can provide valuable evidence about the type of tool used for the dismemberment, and guide investigators in the search for a weapon. The burning process leads to dehydration of the bones, but the relative pattern of the cut marks may still be maintained.
One of the more disturbing recent cases where a burned body was found by investigators occurred earlier this year in Cincinnati, Ohio. The foster parents of a three year old disabled child reported him missing a week after they had returned from a family reunion is Kentucky. Hundreds of police and volunteers searched the area for several days, but to no avail. Police then discovered that the foster parents, not wanting to take the boy to the reunion, had wrapped the child up like a cocoon and left him in a closet for two days while they went to Kentucky. When they returned, the boy was dead. While others were searching for him, they apparently went in the next county, attempting to conceal the crime by burning the body repeatedly--two or three times.