The return address on the letters read simply: “Broadmoor, Crowthorne, Berkshire.” But what they contained was a treasure trove of illustrative quotations for Dr. James Murray, the first editor of what would eventually become The Oxford English Dictionary (OED). Compiling a comprehensive dictionary — a project Dr. Murray and his colleagues were engaged in during the late 19th century — requires, rather like Wikipedia today, an army of volunteer contributors, some more competent than others. Rare is the volunteer like Dr. W.C. Minor of Broadmoor who can provide tens of thousands of illustrative quotations for OED entries, and even deliver examples for certain desired words on demand.

Rarer still is the valued contributor who is also a certified lunatic and murderer. But that’s exactly what William Chester Minor was, though it would take Dr. Murray nearly a decade to learn the true identity of his angel wordsmith.

The full address of Minor’s residence was Cell Block Two at the Broadmoor Asylum for the Criminally Insane. He may have been a guest of the English authorities, but Minor, born in 1834, was actually an American, descended from a distinguished family of Connecticut aristocrats. A clever young man with all the advantages life has to offer, Minor earned a medical degree from Yale in 1863, and the young surgeon enlisted in the Union Army just four days before the historic battle of Gettysburg. But, as Simon Winchester chronicles in the best-seller The Professor and The Madman, Minor was a sensitive, gentle man, not one cut out for soldiering and the horrific scenes he witnessed on the front lines of the U.S. Civil War, including at the bloody Battle of the Wilderness.

Murray assumed that his favorite volunteer was a somewhat reclusive doctor at the asylum.

After the war and less than a decade before he would arrive at Broadmoor, Minor continued to rise in the Army ranks, becoming a captain and regarded by some as one of the best surgeons in the country. But his behavior became increasingly erratic and unpredictable; he grew paranoid of plots against his life and spent most evenings frequenting prostitutes in the Tenderloin districts of New York and other cities where he was stationed. Army doctors concluded he had been “incapacitated by causes arising in the line of duty” — what we would call post-traumatic stress disorder today. After being released from the Army, Minor left for London in 1871 with his books and watercolor paints in the hopes of starting a new and more peaceful life.

What he found instead were the same old fears and delusions. One night in February 1872, Minor, convinced that someone was trying to break into his room, wandered into the streets of London with a gun and shot and killed an innocent man in cold blood. Found not guilty by reason of insanity, Minor was committed as a “certified criminal lunatic” to Broadmoor, where he would spend most of the next 40 years.

The well-heeled former Army surgeon enjoyed some special treatment at Broadmoor, including a two-room suite in which one of the cells was lined floor to ceiling with books, Minor’s passion and solace. And when James Murray, a Scottish lexicographer, sent out a press release in the early 1880s asking for readers to assist with the painstaking work of finding example passages to accompany the great dictionary’s definitions, Minor quickly volunteered, though it would be years before they received his first submission.

With nothing but time on his hands, and buoyed by the chance to contribute once again to society, Minor pursued the enormous task — but from an unusual angle. His was “a working method,” writes Winchester, “that turned out to be different from that of all other volunteer readers, but that soon marked him as uniquely valuable in the making of the great dictionary.”

Meticulously combing over his private library, Minor wrote down every single word of interest as he came to it, making extensive annotated word lists that took years to compile. Minor’s system meant that rather than just sending in quotation slips for rather arbitrary words (as most volunteers did), the committed inmate could find out which words Murray and the OED editors needed examples for and then supply the relevant quotations — tens of thousands of them over the years.

For almost a decade, Murray assumed that his favorite volunteer was a somewhat reclusive doctor at the asylum who had spare time on his hands, even if it was a bit odd that he consistently declined invitations to attend events at Murray’s Oxford headquarters less than 40 miles from Broadmoor. When Murray finally learned the truth about his volunteer, from a passing remark made by a Harvard librarian who knew Minor’s backstory, he set out to visit Broadmoor in 1891. And for the next two decades, Murray continued to visit Minor, and the two men developed a longstanding friendship. “So enormous have been Dr. Minor’s contributions during the past 17 or 18 years,” Murray said of his lunatic friend’s accomplishments in 1899, “that we could easily illustrate the last four centuries from his quotations alone.”

In the end Minor’s illness did not appear to compromise the integrity, or enormous utility, of his lexicographic work for the OED project — demonstrating yet again how in certain human undertakings, there can be a fine line between madness and innovation.