<P> Jimmy and his friends get Dave drunk at a local bar . When Dave leaves the bar, the men follow him out . Jimmy tells Dave that he shot "Just Ray" Harris at that same location for ratting him out and sending him to jail . Jimmy informs Dave that his wife thinks he murdered Katie and tells Dave he will let him live if he confesses . Dave repeatedly tells Jimmy that he did kill someone but it was not Katie: he beat a child molester to death after finding him having sex with a child prostitute in a car . Jimmy does not believe Dave's claim and threatens him with a knife . When Dave finally admits to killing Katie thinking he can escape with his life, Jimmy kills him and disposes of his body in the adjacent Mystic River . </P> <P> While Dave is being killed, Brendan (having found out about his father's gun during questioning) confronts his younger brother Ray Jr. and his brother's friend John about Katie's murder . He beats the two boys and threatens to kill them if they do not admit their guilt, but when John takes the gun and is about to shoot him, Sean and Powers arrive just in time to stop it . </P> <P> The next morning, Sean tells Jimmy the police have Katie's murderers--who have confessed . She was killed by Brendan's brother, "Silent Ray" Harris, and his friend John O'Shea in a violent prank gone wrong: The kids got hold of Just Ray's gun and saw a car coming which happened to be Katie's . John aimed the gun just to scare her but the gun went off by accident . The car veered onto the curb and Katie got out and ran into the park . Silent Ray and John pursued her so she wouldn't tell anyone . The beating Katie received was from Silent Ray, who had a hockey stick . Once she was beaten, John shot her again, killing her . Sean asks Jimmy if he has seen Dave, because he is wanted for questioning in another case, the murder of a known child molester . A distraught Jimmy thanks Sean for finding his daughter's killers, but says, "if only you had been a little faster ." Sean asks Jimmy if he's going to "send Celeste Boyle $500 a month too?" </P> <P> Sean reunites with his wife and his daughter Nora, after apologizing for "pushing her away". Jimmy goes to his wife, Annabeth and confesses . She comforts him and tells him he is a king and kings always make the right decision . At a town parade, Sean sees Jimmy, and mimics shooting him, to let Jimmy know he is watching . </P>

Who killed the girl in mystic river movie