My initial Noir ideas

The film begins with man, who you later discover to be a detective, walking into his home from work. As he stumbles up his steps to open the front door, it begins to rain and he then thinks about what has happened to him over the past few days.
On the first day he was investigating the murder of a businessman, when he meets his attracting but deadly wife, who he is suspicious of. He investigates further and discovers that her husband had recently made a fortune and that he had many enemies whom wanted to see him dead. As he goes deeper into the mans history, he discovers three main suspects. The first used to be his partner in business, the second is a man who he had business dealings with and the third is a rival businessman.
He starts to follow up the three men and trace them to where they are now. He discovers that two of the men are also dead, murdered by an unknown killer. The third is living locally, and that is his old business partner. He then goes to meet the man, when he arrives he is greeted by the man, and shown to the front room, where he realizes someone else is in the house. He proceeds to the bedroom to find the dead mans wife sleeping in the bed of the suspect. He goes back and tells the man that he knows what is happening and that he will prove them guilty when he finds the right proof. He goes back to the murder scene, looking for anything that may prove him right, as he wanders round the room he noticed a cigar end on the floor of the house, knowing from information that his wife gave him that he wasn’t a smoker he had his lead. He then gets all the information he can from the cigar and reveals that the man was there the night the man was murdered. He had him, and now to catch his wife, this was harder so he then examined the mans body, only to notice three discreet scratches with nail vanish on them. The second he made clear that was hers he races to the house closely followed by the police. Only to discover that the man and woman had fled, taken only the necessaries and left, he knows there is no way to trace them, gone without a trace.
So he closes the case and returns home when it flashes back to the beginning, as he stands on his steps a car pulls up, the window is rolled down and the detective is shot and killed on his own doorstep. Then it fades black.
The major focus points of the opening scene is that, the detective looks exhausted and as he strolls up the street to his home, he stops and looks down the winding streets as it begins to rain. He wanders up the step to his home and drops his keys as he bends down to pick them up he thinks about the last week and what has happened to him. As he stands up he hears a car coming up the street and that’s when he goes into the past in his mind.
To begin with, the sound should be slow depressing music as he walks down the darkly light street holding his jacket over his shoulder looking dirty and careless. As he moves towards his home the light comes in and the music changes to a happier tone, but when it rains it goes back to a darker mood.