Gaslight (1940)

Gaslight is a 1940 British psychological thriller film directed by Thorold Dickinson which stars Anton Walbrook and Diana Wynyard, and features Frank Pettingell.

Set in Pimlico, London, Alice Barlow (Marie Wright) is murdered by an unknown man, who then ransacks her house, looking for her valuable rubies. The house remains empty for many years, until newlyweds Paul and Bella Mallen move in. Bella (Diana Wynyard) soon finds herself misplacing small objects; and, before long, Paul (Anton Walbrook) has her believing she is losing her sanity. B. G. Rough (Frank Pettingell), a former detective involved in the original murder investigation, immediately suspects him of Alice Barlow's murder.
Paul lights the gas lamps to search the closed-off upper floors, which causes the rest of the lamps in the house to dim slightly. When Bella comments on the lights' dimming, he tells her that she is imagining things. Bella is persuaded that she is hearing noises, unaware that Paul enters the upper floors from the house next door. The sinister interpretation of the change in light levels is part of a larger pattern of deception to which Bella is subjected. It is revealed that Paul is a bigamist. He is the wanted Louis Bauer, who has returned to the house to search for the rubies he was unable to find after the murder.