'TMZ Presents: Killing a Movie Star: Grave Injustice' Now on YouTube

Dominique Dunne's star was on the rise -- fresh off the "Poltergeist" movie spotlight -- when tragedy struck ... she was strangled to death by her jilted ex, a chilling Hollywood story that still stuns.

"TMZ Presents: Killing a Movie Star: Grave Injustice" dives into the 1982 murder of Dominique at the hands of her ex, John Sweeney ... and how, after a shocking miscarriage of justice, he went on to terrorize again -- and it's now available to watch on YouTube.

The grave injustice points to Sweeney’s shockingly light sentence -- he was convicted of manslaughter and walked free after just two and a half years in prison ... despite massive public outcry and protests over the verdict.

In the primetime special, we also sit down with Dominique’s brother, Griffin Dunne ... and we confirm his lingering suspicion that Sweeney went on to abuse again -- including a 2000 case when a woman filed a restraining order against him, detailing shocking brutality.