The Thin Blue Line

Errol Morris is one of the best documentarians around. His The Fog Of War is a great milestone in the genre.

But his most important film will likely always be 1988's The Thin Blue Line, which helped free a wrongly convicted man of murder. It's very good, not great, but the seeds that came to fruition in later Morris works like The Fog Of War were sown here.

Here is a trailer link.