When internal affairs investigators asked Officer Daniel Pantaleo in 2014 to define a chokehold, he described a scenario where “you use your forearm, grasped with the other hand, and you pull back with your forearm onto the windpipe preventing him from breathing.”

Investigators with the New York Police Department then had him watch video that showed him standing behind Eric Garner during a botched arrest five months earlier on Staten Island.

In the video, Mr Pantaleo had his left forearm wrapped around Garner’s neck, hands clasped. Still, he denied having used the prohibited manoeuvre.

“No, I did not,” Mr Pantaleo said.

An administrative judge, in a 46-page opinion obtained by The New York Times, found this explanation “implausible and self-serving.”

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The judge, Rosemarie Maldonado, who has recommended that Mr Pantaleo be fired, concluded that he had been “untruthful” during the interview, according to the opinion that grew out of a departmental trial that ended in June.

Ms Maldonado, a deputy commissioner with the Police Department, also found that officers who testified in Mr Pantaleo’s defence were “unhelpful or unreliable.”

A final decision about Mr Pantaleo’s fate rests with the police commissioner, and will come five years after the death of Garner — who uttered “I can’t breathe” 11 times — first galvanised the Black Lives Matter movement.

Ms Maldonado said the video of the 17 July 2014 encounter and an autopsy that found fresh haemorrhaging in Garner’s neck muscles provided “overwhelming” evidence that Mr Pantaleo had used a chokehold despite being trained not to.

However troubling, she said she was not convinced that it was his intent to choke Garner and she acquitted the officer of strangulation.

Mr Pantaleo’s “use of a chokehold,” she wrote, “fell so far short of objective reasonableness that this tribunal found it to be reckless — a gross deviation from the standard of conduct established for a New York City police officer.”

Mr Pantaleo did not testify in his own defence during the departmental trial.

The judge’s finding that Mr Pantaleo was “untruthful” underscores a broader problem with the credibility of police accounts about interactions with civilians, particularly in high-profile cases.

Police Commissioner James P O’Neill is expected to decide by the end of the month whether to dismiss Mr Pantaleo, as Ms Maldonado recommended, or to take less drastic measures. The controversy has become central to Bill de Blasio’s tenure as mayor and his campaign for the Democratic presidential nomination.

Mr O’Neill is also expected to consider responses to the ruling from Mr Pantaleo’s defence lawyer, Stuart London, and the Civilian Complaint Review Board, the city agency that prosecuted the case under an agreement with the Police Department.

Mr Pantaleo has been suspended since 2 August. He has spent the last five years on desk duty on Staten Island while the criminal and disciplinary processes played out.

Protesters mark the five year anniversary of the death of Eric Garner, who repeated the phrase "I can't breathe" almost a dozen times while being arrested for an alleged misdemeanor (Getty Images)

Mr London did not answer phone calls and text messages seeking comment on Sunday.

Albert W O’Leary, a spokesperson for the Police Benevolent Association, declined to comment.

Five days before Mr Pantaleo’s 2014 interview with internal affairs, a grand jury on Staten Island declined to bring criminal charges against him. And on the eve of the fifth anniversary of Garner’s death, the US attorney general, William Barr, ordered the federal civil rights investigation to be closed without charges.

Mr Pantaleo was not the only officer whose testimony during the departmental trial Ms Maldonado deemed questionable.

Officers Mark Ramos and Craig Furlani responded to the scene in the Tompkinsville neighbourhood of Staten Island, but testified that they did not note the positioning of Mr Pantaleo’s arms, Ms Maldonado said.

Officer William Meems, who arrived after Garner was on the ground, said at the trial that he did not “focus on any one spot.”

Mr Pantaleo’s partner, Justin Damico, who can be seen in the video stretching his hands between Garner’s head and Mr Pantaleo’s face, claimed he had “no focus” on what his partner was doing.

“The more central the factual inquiry was, the more vague recollections became,” Ms Maldonado said. She did not say whether she believed the officers were truthful, or if they should be disciplined.

Instead, she focused on a nine-second portion of a video filmed by Ramsey Orta, Garner’s friend, that she said was pivotal to proving not only that Mr Pantaleo had violated police rules, but that his conduct was a crime.

Two and a half minutes into the video, Mr Pantaleo and Garner fell away from a plate-glass window to the ground. Mr Pantaleo’s left arm was around Garner’s neck while they were both on the Bay Street sidewalk.

Mr Ramos and Mr Furlani had arrived, giving Mr Pantaleo other options to gain compliance and adjust his grip, Ms Maldonado said. But instead of letting go, he clasped his hands.

Two seconds later, she said, Garner gave what appeared to be the first signal of distress: He opened his right hand with his palm out and made a guttural sound.

His suffering was confirmed, she said, when Garner, on his side with his left arm behind his back and his right hand still open and out, coughed and grimaced as Mr Pantaleo maintained his grip.

At that moment, she said the officer’s conduct “escalated from a Patrol Guide violation to criminal recklessness,” she said.