Any of the Peter Ustinov Poirots, Albert Finney's Murder on the Orient Express, Jeremy Brett version of Sherlock Holmes or Peter Cushing as Holmes in Hound of the Baskervilles.
Several episodes of the 70's run of Columbo are very good, A Friend In Deed, The Conspirators, Make Me A Perfect Murder, Murder By The Book. Then you have all the other classic US detective shows, all have great episodes and lesser ones.
Hitchcock, so many to choose from, avoid Psycho, great film, not gory but a masterpiece in scary! North By Northwest is a good yarn.
Joan Hickson as Miss Marple or for a lighter touch Margaret Rutherford in the same role.
From older british TV Anthony Quale as Adam Strange in Strange Report, an early CSI type forensics format, or chuck in a bit of supernatural Randal & Hopkirk. Then you have stuff like Bergerac, Shoestring etc... from the 80's.
More up to date Aurora Teagarden, Canadian/American co-production, very well produced and in no way offensive / scary.
Most of the above can be found on TV scedules throughout the year.