Mystic River ending explained

What happens

Jimmy kills Dave, believing he murdered Katie. Then Sean learns two other local men did it, and Dave was innocent. Jimmy is never charged, and at the parade Sean can only signal that he knows.

The last image

The neighbourhood parade goes on, the crowd celebrating while Sean silently signals Jimmy that he knows and Annabeth stands firmly beside her husband.

What it says

The ending shows a community that protects its own and lets a wrong go unspoken. Jimmy's grief hardens into certainty, and the film leaves you to judge what the neighbourhood is willing to ignore.