Thanks for the info, nenslo. It turns out the Slaughter "Murder in the Red Barn" (1935) is available on YouTube:
https://www.youtube.com/watch?v=iNFpvX-isuk
I also discovered there were several silent versions of the story, the first being in 1902. In 1908 a ten-minute short known as both "The Red Barn Crime" and "Maria Marten" was directed by William Haggar and starred him and Violet Haggar. On IMDB there's a comment from Violet's grandson identifying William as his great uncle. Other silent versions were filmed in 1913 and 1927. The earliest productions seem not to have survived, but I found a post by someone who'd watched the 1927 film years ago on VHS.
Link to the book:
Thriller Picture Library 171