A method of detecting minute amounts of arsenic had been discovered four years before, and this technique led to Marie's conviction. Criminalistics is the analysis, comparison, identification, and interpretation of physical evidence or clues. The criminalist uses physical and natural sciences to examine physical evidence and prove the existence of a crime or make connections. The criminalist may work with evidence so small that a scanning electron microscope is needed to see it, or with evidence as large as a building. Forensic pathology involves the study of disease.
Forensic pathologists seek to determine what caused a person's death.
This is done by the examination of the body at an autopsy. Autopsies are ordered when deaths are due to homicide, accident, or suicide, and may also be performed in cases of sudden death of an apparently healthy person, among other cases. The forensic pathologist's investigation may include gathering information at the scene of death for examination. The forensic pathologist works in coordination with other forensic professionals. They may send evidence to a criminalist to be analyzed, specimens to a toxicologist for study, bullets and other evidence to a ballistics expert for examination, or rely on a forensic odontologist for dental identification.