John Christopher Lenehan (1889-1943) was born in County Longford, Ireland, and took up writing crime fiction while teaching. A detailed biography of Lenehan and an analysis of his work can be found on the Promoting Crime blog here: https://promotingcrime.blogspot.com/2016/11/jclenhan-1889-1943.html
See also http://www.classiccrimefiction.com/jc-lenehan.htm for a bibliography and a biography written by Lenehan’s granddaughter. The Long Eaton Advertiser newspaper of Derbyshire, England, ran a long obituary of Lenehan on June 5, 1943, on page 3. It noted his involvement in the local Catholic church and in his school’s sports as well as writing.
Lenehan had two series characters, Detective Inspector Kilby of Scotland Yard and Charlie Ryan. The Crime & Mystery Fiction website has a bibliography of Lenehan’s work sorted by lead character: https://embden11.home.xs4all.nl/Engels8/lenehan.htm
The first Kilby title is The Tunnel Mystery published in the UK by Herbert Jenkins in 1929. It was released in the US by the Mystery League in 1931. Both Black Heath Classic Crime and Oleander Press have reprinted it. It is a nicely complicated mystery but far too long.
Mr. David Hyde, a jeweler from London, settled into a third-class compartment on a train leaving Yorkshire after acquiring a fabulously expensive diamond necklace in a private sale. His companions included the proprietor of a pub, a young lady traveling alone, two secondary school students, two women returning from a shopping expedition, and a tall nondescript man. Everyone was hale and hearty as the train entered a long dark tunnel. As it emerged into daylight, the jeweler was dying, obviously shot. No one in the train car admitted to hearing the gun or seeing a flash. The weapon was nowhere to be found.
When the authorities examined the crime scene, the diamond necklace was missing and they found a broken window in the compartment, raising the possibility that the shot had come from outside the train. The likely motive was the theft of the necklace, as a gang of jewelry thieves was known to be active in the area.
The local police did what they could but after a few days the Chief Constable called in Scotland Yard, and Detective Inspector Kilby arrived a day later. He found himself as befuddled as the locals and they jointly sorted through the various clues and conflicting interviews to arrive at a tidy solution.
Identity plays a role here, as well as an announced intention to change a will. Hyde had threatened to disinherit his daughter if she insisted on marrying a man of which he disapproved, providing two immediate suspects in his death, although neither of them were present. Anyone rash enough to openly plan to change his or her will in Golden Age crime fiction is certain to be killed before the change can be implemented.
Almost too many characters to keep track of with some good misdirection folded into the narrative. One of the criminals was apparent early on although his role wasn’t clear. Clever solution to the murder method. Devotees of locked room plots will want to look at this one.