Eric Garner's mother, Gwen Carr, center, with the Rev. Al Sharpton and others after a disciplinary hearing for Daniel Pantaleo.
New York CNN  — 

Tensions were high outside NYPD headquarters on Thursday as Eric Garner’s mother and attorneys for the NYPD officer seen with his arms around Garner’s neck just before Garner died more than four years ago left the first hearing in the disciplinary process for the officer.

The disciplinary trial that could determine whether the NYPD officer, Daniel Pantaleo, can remain on the force is set to begin on May 13 and is expected to go on for 10 days. A grand jury decided not to indict Pantaleo in 2014, and he does not face any criminal charges.

Garner died in July 2014 after police attempted to arrest the 43-year-old father, who was allegedly selling cigarettes illegally in Staten Island. His death became emblematic of longstanding tensions between police and minority communities.

Pantaleo was one officer seen on video wrapping his arms around Garner’s neck before he complained he couldn’t breathe and died. Pantaleo has remained on the department’s payroll for the past four years.

Garner’s mother, Gwen Carr, told reporters outside NYPD headquarters after the meeting that she had “mixed emotions” over being in the same room as Pantaleo.

“I felt sort of numb being in the same space as my son’s murderer,” Carr said. “We would have liked to seen it (the trial) much earlier but I am just glad that this is moving forward.”

Dates for the trial were set Thursday during a hearing involving Pantaleo’s representation and the Civilian Complaint Review Board, a police oversight entity that will serve as the prosecution in this trial. CCRB Chairman Fred Davie said his office stands ready to prosecute Pantaleo and that his office will bring forth evidence to prove that Pantaleo used “excessive and unnecessary use of force.”

As many as 26 witnesses are expected to be a part of the trial, half from the prosecution and half to be called from Pantaleo’s defense. Both sides are expected to give updates on the availability of witnesses on January 31.

Pantaleo’s attorney, Stuart London, told reporters after the meeting that a defense medical expert will testify there was no chokehold, and that Pantaleo’s arm was not around Garner’s neck when he said “I can’t breathe.”

“If you look at the video frame by frame it’s a very different video than if you view it once in real time,” London said. “The problem is we need to educate both the media and the public that not only was there never a chokehold, but officer Pantaleo was just making a simple arrest using a seat belt technique.”

Pat Lynch, president of the Patrolmen’s Benevolent Association, told reporters, “We are having a trial in front of a kangaroo court.” Protesters chanted “Pantaleo has got to go” as he spoke.

“All we ever ask for as New York City police officers is for fairness,” Lynch said. “We are going to bring forth evidence that Officer Pantaleo did exactly what he was trained to do.”

After the grand jury’s 2014 decision, the NYPD said it would keep its disciplinary process on hold until the Justice Department decided on whether it would charge Pantaleo. But in July, the NYPD’s then-deputy commissioner of legal matters wrote a letter to the Justice Department saying that an “extraordinary” amount of time had passed, and the NYPD would no longer delay its internal proceedings.

NYPD Commissioner James P. O’Neill said earlier this week the department wants the case to move as efficiently as possible. “We do want to get this done. … I know it’s been a long time.”

The NYPD said it would also launch disciplinary proceedings against Pantaleo’s supervisor, Sgt. Kizzy Adonis, who is still on active duty.

CNN’s Sonia Moghe contributed to this report.