Search two Crimes/Thriller from the 50s/60s years, acquitted, citation

Hello to all you  Reader,

a fabulously suspenseful rare 
unknown Thriller (French/British?) in which a man pushes his 
wife down a ravine while she is taking pictures with her camera.Even as she falls, she turns andtakes photos of the murderer, 
of her husband.Of course he immediately climbs down into the gorge, but cannot find the camera. The inspector 
later identifies the 
perpetrato through the photos.I was already thinking of "Le meurtrier" (The Blunderer),by 
Patricia highsmith,unfortunatelyit wasn't that one.2) Probably a us production, fordiscerning crime film lovers, 
wanted film is under the motto: "Two lies that make one truth"The suicide note from a long-
dead woman reveals the following:her daughter had been murdered 
by her husband (i.e., the 
writer's son-in-law); but he 
was acquitted. When the mother 
fell ill (and probably saw her 
end near),she poured poison 
into a water bottle, wiped her 
fingerprints off and asked her 
son-in-law to serve her a glass of water. He was then sentenced to death, the discovery of the
letter came too late for him.Closing words (voice of the 
older woman): "Two lies that 
make up one truth."I am very grateful for reading 
any kind of help.greeting

Maximilian