Dominique Dunne's Killer Boyfriend Allegedly Terrorized Others After Murder Trial

The trial of the boyfriend of actress Dominique Dunne -- one of the stars of "Poltergeist" -- stands out as one of the most appalling miscarriages of justice ... and what unfolded in the aftermath of the 1982 murder is especially unsettling -- all exposed in our new FOX primetime special ... which unearths shocking new evidence.

In the harrowing doc airing Monday night, we confirm Griffin Dunne's lingering suspicion his sister's killer, John Sweeney, had committed more domestic violence after the trial -- one particular case from 2000 ... when a woman filed a restraining order against him, alleging shocking brutality.

Too scared to speak on camera, the woman speaks directly to Harvey Levin ... recalling how he dragged her by her ponytail through a hotel lobby, shoved her head in a bathtub, pushed her against a wall, and put his hands on her collarbone near her throat.

She escaped with their infant child and hasn't seen him since ... and despite getting the police involved, Sweeney wasn't charged with a crime.

Charles Wessler, an Oscar-winning producer and family friend of the Dunnes, says the recent revelations don't come as a surprise ... claiming Sweeney still caries the same volatile rage to this very day. Dominque's devastated pal Gloria echoes the sentiment, saying he was never cured ... calling him a caged animal.

Harold Johnson, the lead detective in the 1982 case, is equally disturbed ... saying it's a travesty a man as violent as Sweeney is still going around choking women.