Ex-con drags screaming woman behind van and pulls down her underwear, police say. Then two good Samaritans show up.

A 27-year-old woman was walking home from a Brooklyn synagogue just after midnight Tuesday when a man approached her and said "hi," police sources told the New York Daily News.

The woman ignored him and continued on her way down the street, but things didn't end there.

Instead, he dragged the woman behind a van and pulled down her underwear, police told the paper, as she screamed, "Help me!"

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But a father and stepson who live nearby and were returning home heard the woman's cry and rushed over to help, police said.

The victim's pants were pulled down to her ankles as her assailant held and shook her, police told the New York Post.

But the dad scared him away and stayed with the victim, the Daily News said. Blood was coming out of her nose and ear, a police source added to the Post, and an ambulance soon arrived.

The stepson chased after the attacker for seven blocks before flagging down police, the Daily News added.

Todd Deas, 31, who lives in a men's shelter, the paper noted, was charged with attempted rape, assault and strangulation, police said.

His rap sheet includes 19 prior arrests, including sealed rape and sexual abuse cases from 1999 and 2001, sources told paper. Deas served three prison sentences and was paroled in July after a 2013 conviction for attempted promotion of prison contraband, the Daily News added.

Deas' arraignment was scheduled for Wednesday, WPIX-TV reported.