The Killers Identity!
It took me a while to decide who killed Sidney and I found it hard to find a character with a good motive.
The Killer Is-Gale Weathers
She couldn't stand Sidney any more. She was dying to get rid of her. Waiting for ten years, no one had yet attempted to kill Sidney again so she thought she would just do it herself. For her own benefit and her and Dewey's daughter.
Maybe some of you don't agree with my killer. But that is how I wanted it to go. I hope you enjoyed my fanfic story.