Unfinished Business by JA Jance

 This is the latest in the always enjoyable Ali Reynolds series. The story starts with a teen committing a murder years earlier--and getting away with it. It then moves on to another teen convicted of a different murder that he swears he didn't commit. While the 2 cases seem unrelated, it turns out that both end up in Ali's orbit for different reasons. One of the now grown men will turn out to be a threat to Ali's team while the other will turn out to be a blessing.

At the end of the book, Jance brings in the title character from one of her other series, JP Beaumont, which was a pleasant surprise.