Nearly five years after he tackled Eric Garner in a fatal encounter that began because Garner was allegedly selling loose cigarettes, New York City police officer Daniel Pantaleo began his disciplinary trial on Monday at 1 Police Plaza.

The trial has been a long time coming for Garner’s family and police reform activists. Garner’s dying words, “I can’t breathe,” became a rallying cry for the Black Lives Matter movement. Pantaleo was never charged criminally, and he is the only officer — of several on the scene that day — to receive a disciplinary trial.

In his opening statement, prosecutor Jonathan Fogel said that Garner did not pose a threat to the public or to the officers. He pointed out that Garner was unarmed, that there was no urgency to the situation, and that Pantaleo could have waited for a backup team to arrive. He accused Pantaleo of using an “unequivocally banned chokehold," and called it “shocking, brutal violence,” that never gets easier to watch.

Prosecutors must prove that Pantaleo acted recklessly and that he intentionally tried to restrict Garner’s breathing. Medical evidence will be important for both sides, and prosecutors plan to call the doctor who performed Garner’s autopsy and ruled the death a homicide. Dr. Florina Persechino is expected to show photos of hemorrhaging and trauma deep into the muscle surrounding Garner’s neck.

The NYPD’s own investigators determined that Pantaleo should face disciplinary charges for his actions. Deputy Inspector Charles Barton testified on Monday that he ordered the lead investigator to prepare disciplinary charges against Pantaleo in January of 2015. It’s unclear why the NYPD never followed through with the recommendation.

In his opening statement, defense attorney Stuart London said that Garner triggered his own death with a combination of his bad health and his decision to resist being arrested. He asserted that his client used a so-called “seatbelt maneuver” and approached Garner from behind, put one arm under his armpit and the other arm over his shoulder.

“The only reason his hand went towards the neck was due to Mr. Garner’s morbid obesity and the fact that he resisted arrest,” said London outside the trial room.”If he didn’t resist arrest we would not be here today.”

Ramsey Orta, the man who used his phone to videotape the confrontation between Garner and police, was the first person to testify. He did so by video conference from state prison. London tried to use Orta’s lengthy criminal history to discredit him (he is currently incarcerated for gun and drug convictions). At one point, Orta said he had been paid more than $15,000 in royalties from the Daily News for his video.

After London cross-examined Orta, prosecutor Suzanne O’Hare asked Orta if he had testified truthfully and Orta responded, “Yes." And then, to make a point, she added, “Is your cell phone video lying?” Orta said, “No.”

The video was played inside the trial room and Garner’s sister, Ellisha broke down crying. Her sobs could be heard from the back row. Gwen Carr, Garner’s mother also got emotional and walked out of the trial room. Outside, she spoke to reporters in the rain.

“It’s been five years,” said Carr. “Five years we’ve been on the front line, trying to get justice — and they’re still trying to sweep it under the rug.”

Carr was surrounded by advocates and the family members of others killed by police. Rev. Al Sharpton also attended the trial by Carr’s side.

Earlier in the morning, a small group of protesters from Black Lives Matter New York shut down part of the FDR Drive to call attention to the long-awaited proceedings. They held a banner that read, “#FirePantaleo.”

“This trial should have happened a long time ago,” said Hawk Newsome, chairman of Black Lives Matter New York. “We’re sick of dying out here in these streets.”

Outside 1 Police Plaza after the day’s hearings, advocates for police reform chanted, “Fire Pantaleo!” as Patrick Lynch, president of the Patrolmen’s Benevolent Association, struggled to be heard.

“Mr. Garner never said he could not breathe while any arm was near his neck,” said Lynch. “What we saw was a legal, trained, seatbelt maneuver.”

Carr pushed back against claims that her son was to blame for resisting his arrest.

“You see how cruel they was,” she said. “Even if he didn’t accept it, they wasn’t supposed to kill him.”

Pantaleo could lose his job at the end of the trial. But even if the administrative judge recommends firing, it is up to the police commissioner to make the final decision about a punishment, if any.

Sharpton said it’s not just Pantaleo on trial, but the credibility of the entire New York City police department.

“Will you allow someone to stay within the police ranks — that is on film, choking a man, and it has been stated that caused his death? That’s the only question left,” Sharpton said.

The trial will continue on Tuesday, and is expected to last around two weeks.

Cindy Rodriguez is an investigative reporter for New York Public Radio. You can follow her on Twitter at @cynrod.

Yasmeen Khan is a reporter covering crime and policing at WNYC. You can follow her on Twitter @yasmeenkhan.