It happened shortly after 3 p.m. Sunday. Two officers were on duty at an L Train platform in Brooklyn.
It started at the entrance, when, police say, the two officers assigned to transit detail followed a 37-year-old man up the stairs who hadn't paid his fare.
"The officers are asking him to stop. The male is refusing to stop at a certain point on the platform. The male, he mutters the words, 'I'm going to kill you if you don't stop following me,'" NYPD Chief of Department Jeffrey Maddrey said.
That verbal threat would become a physical one as the suspect pulled a knife from his pocket.
"They give numerous commands. The male basically challenges the officers, 'No, you're going to have to shoot me,'" Maddrey said.
The confrontation moved inside a train that had just pulled into the station, and that's where police did open fire, after using a Taser on the suspect didn't work.
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The bullets that flew inside the car and onto the platform struck the suspect and two passengers - a 26-year-old woman and a 49-year-old man - as well as a 40-year-old officer.
The officer was rushed to a nearby hospital, where the mayor and new interim police commissioner paid him a visit. They blamed the knife-wielding suspect they called a "career criminal," with more than 20 arrests.
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"Make no mistake, the events that occurred on the Sutter Avenue Station platform with the results of an armed perpetrator who was confronted by officers doing the job we asked them to do," interim NYPD Commissioner Thomas Donlon said.
The 37-year-old suspect was critically injured and is hospitalized.
The 49-year-old passenger was shot in the head during the incident and remains in critical condition.
A 26-year-old woman was grazed by a bullet and remained hospitalized early Monday.
Donlon said this is what the NYPD and MTA have been asking officers to do - to stop the fare evasion that is costing billions of dollars.
Detectives from the department's Force Investigation Division are going through video to determine the trajectory of those bullets. It is possible that the round that struck the officer was his own and ricocheted off the inside of the train.
The officer has been with the NYPD for 10 years, and is expected to recover.
Charges are pending.