by Jack El-Hai, Wonders & Marvels contributor
During the summer of 1951, the St. Petersburg (Florida) Police Department needed help. On July 2, 67-year-old woman named Mary Hardy Reeser had burned to death in her apartment, and the police did not know how or why. A fire of unknown origin had reduced her body to fine ashes — except for her skull (“shrunken to the size of a teacup”), a small section of backbone, and her left foot, which still wore a shoe. 
A chair, end table, and small rug had been incinerated, and the ceiling was darkened by smoke, but otherwise the apartment appeared little affected by the intense heat necessary to transform a human body into cremains.
Stalled in his department’s investigation, police chief J.R. Reichert asked for the FBI’s help and shipped to Washington several pieces of evidence, including clothing fibers, glass fragments found in Reeser’s ashes, particles of her bones, an unburned section of the rug (“heavily soaked with greasy substance”), chair springs, and the shoe. He asked the FBI to investigate these items and to provide “any information or theories that could explain how a human body could be so destroyed and the fire confined to such a small area and so little damage done to the structure of the building and the furniture in the room not even scorched or damaged by smoke.”
Many people had speculated that Reeser’s death was an example of spontaneous human combustion (SHC), a phenomenon that had occurred in novels of Charles Dickens, Herman Melville, and Frederick Marryat, and also in unverified factual cases around the world in which people appeared to have caught fire without a known source of ignition. Could SHC explain Reeser’s fiery death?
The FBI scrutinized the evidence and thought not. Its analysts speculated that an outside source, such as a burning chair or clothing, had set Reeser aflame. “Once the body starts to burn there is enough fat and other inflammable substances to permit varying amounts of destruction to take place,” the FBI noted. “Sometimes this destruction by burning will proceed to a degree which results in almost complete combustion of the body.” The heat from the burning body rises, possibly leaving intact most of the smoldering fire’s surroundings.
The Reeser case continued to receive press attention for years, and citizens sent to the police and FBI their own theories on her death. These attributed the cause of the deadly fire to the use of an oxy-acetylene torch, a murderer who cremated Reeser elsewhere but moved her remains back to her apartment, a form of cancer that creates high temperatures in the body, and of course SHC, among other speculations.
The St. Petersburg Police concluded that Reeser had fallen asleep while smoking, accidentally igniting her rayon nightgown and the chair on which she was sitting. They closed the case soon after receiving the FBI analysis.
Further reading:
The FBI’s file on the Reeser case.
Nickels, Joe; Fischer, John F. (March 1984). “Spontaneous Human Combustion.” The Fire and Arson Investigator 34 (3).