He Jia is dead and we don't know who the murderer is.
When he opened his eyes, he found that he was alive in another place, and the murder had happened seven days ago.
He is the living one, and he is the dead one.
Time is still going backwards, until it goes back to the day of the crime, and He Jia experiences death for the second time.
The second time he opened his eyes, still seven days later, the way of death had changed.
He Jia took the hand of Captain Ren Chengyun, who was in charge of the case: "Actually, I come from a parallel world..."
Ren Chengyun: "Do you think I'm a fool?"
He Jia died for the third time, and when he opened his eyes for the third time, he saw Captain Ren being slapped in the face.
Ps:
1. It involves suspense, but it is not a criminal investigation story.
2. The whole text is fictional, future science fiction, reality-oriented.
3. The relationship between attacker and receiver develops slowly, but it is true that both parties fell in love with each other at first sight!
Intention: Hard work will pay off