"It's a horrendous act that we all condemned in policing throughout the country," he said. "But there are 800,000 law enforcement officers throughout this country that are paying the price for the actions of those four cops in Minneapolis."
Monahan, who was part of the NYPD leadership during Eric Garner's in-custody death on Staten Island, said he understood the outrage that fueled protests in New York, Minneapolis, and other cities across the country.
The NYPD issued 72 summonses and arrests Thursday for everything from felony assault on police officers to obstruction.
An officer ended up with a concussion after a garbage can was thrown at him, and a second also wound up with a concussion after he was thrown to the ground.
"This was a very unique crowd last night, more interested in confronting the police, throwing bottles at the police, then they were in protesting," Monahan said. "This was a crowd bent on creating mayhem."
The NYPD expects a different outcome Friday when protesters including Garner's mother Gwen Carr rally in Lower Manhattan.
"She has been involved in lots of protests, and they've never been a problem," Monahan said. "Will there be a small group that may try and cause trouble? If there are, we will have more than enough resources out there to contain it."
Separately, Monahan said the NYPD is "working hand in hand" with the Manhattan District Attorney's office whether to charge the white woman involved in a racially charged encounter in Central Park with a black man.
"To make an arrest, we have to make sure the Manhattan District Attorney's office is willing to prosecute," Monahan said, adding that Amy Cooper was "wasting the time of NYPD officers...something we condemn completely."
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