Those occupants were the four plainclothes officers who followed Grays to his delivery stop, according to Adams. The video shows the officers tell Gray to "stop resisting." They then take him away in handcuffs, leaving his mail truck unattended.
Yelling at the unmarked car about driving recklessly "is the only action that Glen did that day that caused those plainclothes officers to stop their vehicle and to show who's the biggest and the baddest, and place handcuffs on an on-duty postal employee who is delivering the U.S. mail," Adams said. "If they would do that to Glen, in his postal uniform, they would do it to any other person of color in this community."
Asked about the incident, the New York Police Department said only that "the matter is under internal review."
Mayor Bill de Blasio "will be in close touch" with New York City Police Department Commissioner Bill Bratton "about this incident's investigation and findings," Monica Klein, the mayor's deputy press secretary, said in a statement.
"We expect all members of NYPD to act professionally and respectfully," Klein said.
Grays, who said he was issued a summons for disorderly conduct, is engaged to a New York police officer he met while on his delivery route, the New York Times reported.
"I don't hate cops," Grays told the newspaper. Pointing to his fiancee, he said: "I'm marrying one."
Adams said the incident has "traumatised" Grays, who has never been arrested or received a summons from police before.
Adams said that Grays did nothing wrong in the video, adding: "It's hard not the believe that the only reason Glen was handcuffed is because [of] the color of his skin."
Grays is African American.
The police department in New York has come under fire in the past for policies that critics said disproportionately targeted people of color.
Fatal encounters with New York City police have brought additional scrutiny to the department: In 2014, an unarmed black man, Eric Garner, died after he was taken to the ground by officers and put in what appeared to be a chokehold. The incident was caught on tape and ignited protests across the country, with Garner's last words, "I can't breathe," becoming a rallying cry.
That same year, a rookie officer fatally shot Akai Gurley, an unarmed black man, in the stairwell of a Brooklyn housing project. The officer, Peter Liang, was convicted of manslaughter and fired from the department.
In 1999, an unarmed African immigrant, Amadou Diallo, was gunned down by four New York City police officers in front of his apartment building, killed in a hail of 41 bullets.
Sonya Sapp, the mother of Glen Grays, said this week that she cried when she watched the video of her son's arrest. He is the eldest of her six sons.
"I worry about all my boys, every minute, every second of every day," Sapp said at a news conference Wednesday.
The video begins by showing plainclothes officers approaching Grays, who is holding a package. Not all of the words they exchange are clear.
"You want my ID? My ID is right there inside of the truck," Grays tells the officers, pointing to the vehicle.
The officers tell him to get his ID. Grays is heard telling them he is delivering his postal route. Two officers physically pull him away from the door. The package, having fallen to the ground, is kicked away by an officer.
Grays is told to put his hands behind his back.
"Stop resisting," officers tell him.
"He almost hit me," Grays says. "I'm not resisting."
"Put [your hands] behind your back, or you're going to get f---- hurt," one officer tells him.
Four officers surround Grays, who repeats, frustrated: "I'm not resisting."
"Get off of me," he says.
The four plainclothes officers eventually lead Grays, handcuffed, to their unmarked black car.
An officer frisks him and puts him in the car.
Bystanders yell at the officers throughout the encounter. Some recognise Grays and call out to him by name. The video ends there.
Adams, the borough president, said that after the police vehicle drove away, it rear-ended another car and that Grays, who wasn't placed in a seatbelt, was injured in the crash.
From the New York Times:
"The driver, who had turned around to taunt him, hit the vehicle in front of them, Mr. Grays said, causing him to bang his shoulder against the front seat. Mr. Grays was then taken to the 71st Precinct station, where he was issued a summons for disorderly conduct that will require him to appear in court. He was then released."
Adams denounced the actions of the officers, saying he was deeply troubled by the treatment of a federal employee and that the "major steps" taken by de Blasio and Bratton to reform police practices haven't gotten "down to the street."
"This could have been another Eric Garner situation if Glen had not responded as calmly as he did," Adams said.
