Film Noir - Idea Two

Our second idea starts with a man walking home alone, after work, carrying a briefcase. This man enters a dark alleyway, where he is shot by an unknown character in the shadows; all you can see of this other character is his hand holding the gun into the light.
This is then followed by the voice of our detective explaining that he has to find out what happened and why...
How it fits in with Film Noir conventions:

• Characters - Unknown killer and a detective
• The use of key lighting to highlight important props, shadows used to conceal charaters' identities.
• Typical plot line as it starts with a murder
• Era appropriate costume and props
• Set in a big city in America, probably New York, at night