Giallo
(2009)

Inspector Enzo Avolfi (Adrien Brody) is investigating a pattern killer later codenamed "Giallo" (also Adrien Brody), who kidnaps beautiful  women and mutilates them before killing him. Celine, the younger sister of Linda (Emmanuelle Seigner) is his latest victim to be. Enzo and Linda team up to find Celine before is too late.

"Giallo" decides to kidnap Linda as well, something that Enzo stumbles on to. Enzo pursues them and gets into a struggle with Giallo, which results Giallo falling to his death. Linda berates Enzo because she believed the killer would of told her where Celine was. Enzo says she couldn't of trusted him because he was a psychotic killer, but Linda screams she should of never of trusted him.

However, unbeknownst to both of them, fate intervenes. A cop walking through a parking garage hears a thumping noise of a nearby taxi with a puddle of blood underneath. It is Giallo's taxi, with the still alive Celine in the trunk. It can be assumed that she survives and is reunited with her sister.

Thanks Spectre!