2 twins; one guy is good and the other bad. Bad twin just got out of jail and wants to ruin good twin's life. Inadvertently murders a mob boss' daughter.

[Dan]

I read this in the late 1990s. So it may have been published late 80s. The bad guy twin gets out of jail and is bitter about the good one testifying against him to put him in jail. He wanted his brother to claim he had raped the girl, which would've confused the jury he thought. He picks up a young girl hitchhiker and murders her. This girl is the daughter of a powerful mob boss, which brings his wraith down on the good guy twin.
The good twin is married and has never told his wife much about his brother. There are a series of flashbacks that reveal the relationship between the 2 brothers. They were super close growing up, and the bad twin even saved his brother's life once by pulling out a broken piece of glass out of his neck, which gave him a scar (their only physical difference). They were succesful swimmers in school.
The bad twin sets about ruining the other twin's life. He shows up to an important job interview in his place after rubbing cheap whiskey into his neck. He breaks into their home and rapes his wife. She notices the lack of the scar on his neck.
The 2 brothers end up caught by the mob boss and they are trapped on a boat. They bond a little and plan to use some method they had used growing up to fight off another group against their captors.