“I don’t think I was treated fairly,” he said last month at his house in a gated community overlooking the Ross Barnett Reservoir. “Is that the way you treat people after 20 years of working like a dog?”

A physician and pathologist, Dr. Hayne, now 71, began performing autopsies in Mississippi in the late 1980s. He served briefly as interim state medical examiner though he was not, as state law required, board certified in forensic pathology. From 1989, when he left the interim post, to 2010, the office of medical examiner was unfilled for all but five years. Dr. Hayne, working as a private contractor, almost single-handedly picked up the slack.

By his own count, he performed as many as 1,700 autopsies some years, in addition to having his own pathology practice. Dr. David Fowler, the chief medical examiner in Maryland and a former chairman of the standards committee for the National Association of Medical Examiners, called the number “beyond defensible.”

Dr. Hayne said that state-appointed medical examiners simply did not have his motivation as a fee-based contractor, nor his work ethic. “How many autopsies could they do?” he said. “They could do one or 500, they get paid the same amount. Is there any incentive to do a heavy load?”

That incentive is at the heart of the challenges filed on behalf of prisoners in recent weeks, most of them by the Mississippi Innocence Project. The cases in those filings are not clear cut, and in all of them there is circumstantial evidence suggesting guilt and innocence. But Dr. Hayne’s testimony was key.

In one case, Dr. Hayne performed an autopsy of a young boy and concluded he had been suffocated. Some weeks after the boy was buried, his 3-year-old brother told the police that he had been killed by his mother’s boyfriend. Officials exhumed the body, and Dr. Hayne had a cast made of the boy’s face. By comparing his initial notes of face wounds with the cast, Dr. Hayne testified, he found it probable that the boy had been suffocated by a large male hand. The boyfriend was convicted.

Image Dr. Steven T. Hayne performed as many as 1,700 autopsies annually from the late 1980s to the late 2000s.

“I saw a very similar case like that on ‘Law & Order: SVU,’ ” said Dr. Andrew M. Baker, the president of the medical examiners’ association and chief medical examiner for Hennepin County, Minn. “I’ve never heard of it in real life.” Dr. Baker said not only was the technique unheard of but so was the ability to speculate from those sorts of wounds about hand size or gender.