An ex-con, defending a reformed paedophile from an angry mob — begins to doubt the man’s innocence.

We need to understand the ex-con's motive.

I wonder if it would be worth, rather than a reformed paedophile, make him a wrongly accused paedophile. Through the events in the film, we can discover that he was actually let off on a technicality or something and the ex-con discovers that perhaps he did do it after all.

I'm seeing an "Assault on Precinct 13" type film.

I think you're right to drop the sister love story. Whilst it's interesting, I ?don't think it's the A-story.

Can you put this into a more conventional format. Inciting incident, protagonist and goal?