A Crime Club Mystery. In 1937, Universal had acquired the rights to select 4 books from the publisher of the pulp whodunits' annual output of 52 novels. This was the second one produced in the deal. A total of 11 Crime Club mysteries would be filmed. The Crime Club deal ended with the release of The Witness Vanishes in September, 1939.
At one point, the sheriff mistakenly refers to two suspects as "Wallace and Simpson". This is a topical pun, referring to Wallis Simpson, the American socialite for whom King Edward VIII had recently abdicated the English throne so they could marry. (He could not wed a twice-divorced foreigner and remain King, so he chose love; they remained married until his death in 1972, 35 years later.)