Here's a reference about timelines:
https://jerichowriters.com/story-timelines/

Why don't you think about what happens in the book: 1. The murder happens. 2. People arrive on scene. 3. Somebody starts gathering clues to solve the murder. 4. Zombies come for the murderer and the story TAKES a TURN. (JK)
But putting the things that happen in chronological order might help. Sometimes we mix them up for the story to be told differently, and having that chronological timeline will help ground you on whatever day you happen to be writing.

A timeline can also help when you think Murder Day was Tuesday but we solved it on Tuesday and it's actually been 10 days since the beginning. They both can't be Tuesday!