All movies starring Irene Bagach

A story about the work of the Scottish police. Two Edinburgh police detectives kill a third and make it look like he committed suicide. The corpse is put behind the wheel of a car, which is thrown off the pier. And nothing would have happened if they hadn't found two corpses when they lifted the car! The second one ended up in the trunk with his hands cut off and his head missing... Why did the cops need to kill a colleague and how would they get out of it now?