Killers don´t look like anyone in particular. People don´t tend to be like you expect. 

Some old couples have lost the spark in their marriage. Complacency (at være for vant til hinanden/tager hinanden for givet.) 

No one really knows each other very well. 

It´s easier to be anonymous in a big city like New York. 

He is starting out the story as a love story. 
He is using different sections to move the story along. 

He is using the slow increase of tension to capture the readers interest.
He is going in to great detail using a lot of adjectives to create images inside the head of the reader. 

Because in this case the flowers symbolize the emotions the man is going through. 
The flowers also further the illusion that the story is a love story. And is gives an insight of how well the man is able to hide his true intensions. 
 It would decrease the amount of tension and it would not further the illusion that the story is a love story. 

- The air was soft and beautiful, the sky was darkening by slow degrees from blue to the calm and lovely violet of dusk. There are people who loves the city, and this was one of the nights that made them love it. 

- “Hey, beautiful!” The young man gave her a half-smile and raised his hand in a wave. 

- This soft spring evening … he was beautiful.

- In spring anyone can be beautiful.

- The air was soft and sweet.

- Summer is the season of dreams.

- This street was a little darker.

- Half a block down he turned into a narrow lane.

- Now the stars where out, gleaming softly, and the lane was dark and shadowy, lined with vague shapes of garbage cans. The young man was alone now – no, not quite.

- It was getting darker now. 

- Beside the dented trash cans, where the cats made alien love in the dark, screaming in love, screaming, screaming.

- Backed away from the dark shadow sprawled on the cobblestones, away from the litter of tea roses by the garbage cans.

- It was full dark now. 

6. The themes of the story are Love, grief, murder, danger and obsession.  The man seems very happy and in love, but he is a murderer who has gone insane after the woman he loved has died ten years ago.