O Estrangulador Misterioso

I saw this film when I was 10 years old and it has haunted me all my life. At first I could only remember a guy waiting in a room for someone to come back, but then there was the idea of a crazy murderer who goes bizerk when it rains and then the memory of all these dummies in the police station and the murderer gets in there somehow, I don;t know how, but as he is in the room someone comes in, a policeman, just to check out the dummies and the murderer goes and sits in a chair so he won't be discovered because he looks like all the other dummies that are sitting there, and as he is sitting he is facing a window...and we see that it is beginning to rain...and there is a close up of his hand gripping the arm of the chair...all this is from my memory of the film as a 10-year old - when I managed to discover what the film was with the use of IMDb and got a video and looked at it - it all seemed pretty harmless stuff - I saw the film in a little cinema in Shaftesbury Dorset with my brother. My parents left us there and had no idea what the film was. The memory of the American streets, and the cars and the black and white quality have all stayed with me...