The ending doesn't make sense to me
Bruno wants to go back to the crimescène on the island to lay down the lighter.
He wants the police to believe that Guy murdered Miriam.
How is that possible?
The body of Miriam has already been found. So the whole island (which is little) has been investigated for clues and proof.
I think it will be very suspicious if there suddenly is proof on the island.
They will know that somebody put it there afterwards.
And how must the police find the lighter? They are not investigating the island.
And there is a lot of tourism on the island.