McCrones work as a microscopist first attracted widespread public attention when he helped exonerate Lloyd Eldon Miller, a cabdriver who had been sentenced to death for the 1955 murder of an 8-year-old girl in Canton, Illinois.  McCrone was able to show that the stains in a pair of undershorts that the prosecution had presented to the jury as blood were actually red paint.  Millers conviction was overturned by the US Supreme Court in 1967.  In later life, McCrone microscopically examined the physical evidence (hairs, fibers, blood, etc.) that led to the conviction of Wayne Williams as the Atlanta child killer.  That work earned him the 1982 Certificate of Merit from the Forensic Sciences Foundation.
On occasion, McCrone was given hair samples of famous people to analyze.  Based on such analysis, he rejected the hypothesis that Napoleon had been poisoned with arsenic, but concluded that Beethoven had suffered from lead poisoning.