The summary is that there is a boatload of evidence that Jason Simpson was the killer and OJ covered up for him... this private investigator walks you through the evidence that he spent 12 years collecting.
Evidence (whether you agree or not) that he presents:
Jason's altered timecard from the night he worked
His history of mental problems
History of Rage disorder
Pictures of him wearing a knit cap like the one found at the scene dated before the killings and pics of him wearing a different one after
His personal diaries filled with entries hinting, but not actually admitting the crime
A box of very personal affects he stored in Public Storage that he abandoned that included a bunch of stuff including a knife that could have been the murder weapon
Etc... etc...
The picture he draws explains a lot of stuff that didn't sit right in the trial, like why OJ's Bronco only had a drop or two of blood, when he should have been covered head to toe, including his shoes.