Nine Times Nine by Anthony Boucher

Ahasver was the leader of the religious group The Children of Light. Ahasver, wearing his trademark yellow robe, declared himself to be the Wandering Jew, and proclaimed that the gospels of the Bible were wrong, and that he preached the true gospel which was written by Joseph of Arimathea and which he had found in a Tibetan lamasery.

Wolfe Harrigan had written a book Fleece my Sheep which exposed religious rackets such as that of Ahasver. On Easter Sunday, Wolfe Harrigan was murdered in a locked room and witnesses looking through a window clearly saw Ahasver in the room but no one saw him enter or leave that room. There were one hundred and eight witnesses who would testify that Ahasver was at the Temple of Light at the time that the murder was committed.

Matt Duncan was a writer who had just been employed by Wolfe Harrigan to help in his research on phony religious groups. The Harrigans were a wealthy family. Ellen Harrigan was quite religious and contributed to Catholic charities especially to the convent of the Sisters of Martha of Bethany for whom she had recently donated funds for a new chapel. R. Joseph Harrigan had been an attorney, but was currently engaged in speaking on politics to many and varied groups. Arthur and Mary Harrigan were the children of Wolfe. Mary had been determined to go into a convent until Sister Ursula of the Sisters of Martha of Bethany talked her out of the idea.  As the investigation of the crime continue, Sister Ursula asked for information which had been found. Indeed, she was the only one who understood a clue which the dying Wolfe had left to the identity of his murderer.

Detective Lieutenant Terrance Marshall was the policeman investigating the case of Wolfe Harrigan's murder. Marshall had been a Rhodes Scholar and an all-American football player. Instead of accepting a teaching position, he had joined the Los Angeles police force as  a patrolman and had worked his way up. Marshall and Matt Duncan joined forces to try and figure out how Wolfe Harrigan could have been murdered in a locked room. They carefully analyzed the various methods in which such a murder could have been committed which were given in the book The Three Coffins by John Dickson Carr. Their analysis, however, failed to find a way that the murder could have been done. It was Sister Ursula who finally figured out how the murder was committed.

This book was written in 1940 with Boucher using the pen name H. H. Holmes. He dedicated the book to John Dickson Carr. Fortunately, it is still in print.