Discrepancy between estimated and actual time elapsed after death of a severed head

A severed head which had been wrapped in seven plastic bags and set in concrete in an airtight insulated plastic box was found approximately 22 months after the occurence of death. Ammonium magnesium phosphate had formed and on the basis of this and other observed postmortem changes, time elapsed after death was estimated to be from 2 weeks to 6 months. The absence of oxygen is thought to have contributed significantly to the great discrepancy between estimated and actual time elapsed after death.