NYPD released surveillance video they say shows five men suspected of raping an 18-year-old woman on January 7, 2016.
Authorities say each of the five men took turns raping the woman.
The dad quickly returned with two uniformed police officers and the suspects ran.
The woman, whose name has been kept private, was treated at a local hospital and has since been released.
The five men were later seen on a surveillance camera entering a bodega near the playground just before the attack.
'I am disgusted and deeply saddened by the horrific attack, ' de Blasio said.
Other residents have told the press that they will have their teenage children try to avoid the park in Brooklyn where the rape occurred.
In a statement on Sunday, police said the father approached a patrol vehicle on the street to report the assaults.
A fifth suspect in the rape remains at-large, Reuters reports.
Police have been searching for five teens who allegedly raped an 18-year-old in a Brownsville playground. The man with the red jacket was also believed to be the one who threatened the father with the gun.
The New York City Police Department have stated that they are unsure why getting help was so hard for the father since the neighbourhood is full of public housing high-rises, multiple stores and delis that he could have used a phone at. Charges were pending against a 14-year-old, 17-year-old and two 15-year-olds.
"There was no delay in the police response", police spokesman Stephen Davis said in a statement.
He added that every possible step would be taken to find the suspects. "I feel bad now knowing why he needed the phone".
The victim's mother tells the Daily News her daughter is OK.
Several people have come forward, like Bernard Briggs, a New York City bus driver, to talk about how unsafe Osborn Playground has become. The park's lights are rarely on, leaving the blue and red playground equipment, creaking swings and blacktop sports fields into deep shadow.
But even with all that, the news of the attack was alarming.
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