President Zachary Taylor and the Laboratory: Presidential Visit from the Grave. This is a brief but interesting account of how President Taylor was exumed in 1991 to determine if his death was due to poisoning. However, testing proved that the President had not been murdered.
From the site:
Shortly after breaking ground for the Washington Monument on July 4, 1850, President Zachary Taylor, a hero of the Mexican War, fell ill. When he died suddenly a few days later, the cause was listed as gastroenteritis--inflammation of the stomach and intestines.
Some historians suspected that Taylor's death may have had other causes, and in 1991 one convinced Taylor's descendants that the president might have suffered arsenic poisoning. As a result, Taylor's remains were exhumed from a cemetery in Louisville and Kentucky's medical examiner brought samples of hair and fingernail tissue to Oak Ridge National Laboratory for study.
In the Chemical and Analytical Sciences Division, Larry Robinson and Frank Dyer headed the Taylor investigation, using neutron activation analysis to measure the amount of arsenic in the hair and nail samples. After placing the samples in a beam of neutrons from the High Flux Isotope Reactor, Dyer and Robinson looked at the gamma rays coming from the samples for the distinctive energy levels associated with the presence of arsenic. Arsenic is among the easier elements to identify through neutron activation and can be detected in a few parts per million. Most human bodies contain traces of arsenic, so the essential issue in the Taylor case was whether the samples from Taylor contained more arsenic than would be normal after 141 years in the crypt.
Working late in the evenings, Dyer and Robinson in a few days calculated the arsenic levels in the samples and sent them to the Kentucky medical examiner for his decision. After reviewing the test results, the examiner announced that the arsenic levels in the samples were several hundred times less than they would have been if the president had been poisoned with arsenic.
This finding acquitted several of Taylor's prominent contemporaries of the suspicion of murder and proved that history and science share a common quest for truth.