Showing Looking for Yesterday by Marcia Muller

Three years ago, Caro Warrick was acquitted for the murder of her best friend Amelia Bettencourt, but the lingering doubts of everyone around Caro are affecting her life. Sharon McCone is confident that she can succeed where other detectives have failed (though at times it's hard to shake her own misgivings about what happened), but when Caro is brutally beaten right at Sharon's doorstep, the investigation takes on a whole new course. How many more people remain at risk until Amelia's murderer is finally caught?