I)
1. The husband must be the murderer
2. Perhaps the murder weapon can’t be a knife
3. The wife can’t be an accomplice. It is impossible.
4. Perhaps the woman must know the criminal.
5. The investigator may be informed about the murder’s identity by now.
II)
The woman must be in the shower because she’s wet. She may be seeing the murderer. She might get killed.
Voilà :) C’est tout ce que je peux faire!