Acting and cast was great no doubt, I won't even talk about it.

My question is, how did the case get cold. Why did the detectives not doubt the victims' husband/father if he bought a large amount of insurance. Typically in other dramas/movies they would suspect the spouse if it has a large amount of insurance.
Also, is it because of the timeline? How did the police not have a piece of evidence like fingerprint when he did the job so poorly like leaving the scene looking like that.

Did his real brother die? Too many unanswered questions for the sake of my curiosity.

For the music, I don't remember anything so I guess it did not stood out.

This is a mystery movie so rewatching would kind of be pointless because you won't be thrilled anymore (IMO). But it is a great twist and turn movie. Highly recommended