The use of foreshadowing (SPOILERS)
I personally thought the use of foreshadowing was brilliant in the film.
1) After Mrs. Paradine drinks the wine, she looks at the portrait of her husband Colonel Paradine.
2) Here is a link to the picture that also foreshadow the ending.
http://www.hitchcockmania.it/filmografia/the_paradine_case/fotofilm/par22.jpg
3) Here is a link to another picture that also foreshadow the ending.
http://www.hitchcockmania.it/filmografia/the_paradine_case/fotofilm/par71.jpg
4) Simon Flaquer tells "This wasn't suicide. This wasn't assistant suicide. It was murder" in the beginning.
Unlike Witness for Prosecution, The Paradine Case is a simple case.
As Anthony Keane (Gregory Peck) explains it, the simple case has only 3 possibilities: Mr. Paradine poisoned himself, Mrs. Paradine did it, or the valet did it.