Eric Garner died after an officer used an apparent chokehold while trying to place him under arrest in Staten Island. View Full Caption New York Daily News

STATEN ISLAND — Prosecutors who presented evidence to the Eric Garner grand jury were stunned and disappointed when the panel didn't indict NYPD Officer Daniel Pantaleo, DNAinfo New York has learned.

The Staten Island prosecutors felt they had laid out a strong enough case to obtain a “criminally negligent homicide” charge against the eight-year NYPD veteran that would ultimately be decided at trial, according to law enforcement sources.

But after three months of testimony and evidence — built around the gut-wrenching viral video of Garner grappling with police and repeatedly telling them “I can’t breathe” — the 23-member panel declined this month to charge Pantaleo in the so-called “chokehold” fatality.

“They were stunned, surprised, taken aback . . . choose your word,” one law enforcement source told “On The Inside.”

“The prosecutors were extremely disappointed, as much as anyone, when they heard there was no indictment,” another source said.

Even Pantaleo expected to be indicted on the criminal negligent homicide charge, sources say. The 29-year-old officer was so convinced he would be charged that his lawyer, Stuart London, had to twice repeat the news to him before it sank in that he would not face a trial.

A spokesman for Staten Island's District Attorney Daniel Donovan declined comment.

Garner died July 17 while being arrested for allegedly selling loose cigarettes in Stapleton. He was put in an apparent chokehold by Pantaleo.

The fatal encounter ignited waves of protests against aggressive police tactics and the NYPD’s reliance on a “Broken Windows” policy of arresting suspects for minor offenses. It also revived questions about whether racism plays a role in police encounters with minorities, even though Garner’s widow has said the tragedy was not racially motivated.

Sources say prosecutors asked the grand jury to consider charges directly related to Garners death: murder, manslaughter and criminally negligent homicide.

They believed it was unlikely that the panel could find “probable cause” to charge the top two serious counts because they would need evidence that Pantaleo had intended to kill Garner while trying to arrest him, or was aware that he was dying and proceeded anyway.

Similarly, they did not ask the grand jury to consider lesser charges such as assault and reckless endangerment since Pantaleo was allowed by law to make arrests.

“Police are allowed to put their hands on you and use necessary force to effect an arrest,” said a lawyer familiar with police fatality and brutality cases.

The Staten Island prosecutors felt that criminal negligent homicide — carrying a maximum four-year prison term — was the most applicable charge.

Staten Island District Attorney Dan Donovan at his St. George office. View Full Caption DNAinfo/Shayna Jacobs

That’s because Pantaleo and the other officers failed to stop their actions when Garner repeatedly said he could not breathe and did not “perceive a substantial and unjustifiable risk” that Garner would die from his actions.

On Aug. 1, the acting Medical Examiner Barbara Sampson — who was permanently elevated to the post last week by Mayor Bill de Blasio — ruled Garner’s death a homicide, caused by a police chokehold.

That “official” finding was quickly seized upon by police critics, civil rights activists and Garner’s family and their advocates.

NYPD Commissioner Bill Bratton initially added to that sentiment when he said a chokehold appeared to be used in the video, although he has recently rolled back that opinion.

But rather than providing clarity, the ME’s findings complicated matters for prosecutors, sources say.

That’s because the ME's office traditionally confines findings to medical and forensic analysis. They determine the cause, such as by gunshot, stabbing or a blow to the head.

Rarely do they point to a specific suspect such as an angry spouse, a gang member or even a police officer as responsible — that’s the work of law enforcement.

Yet in the Garner case, the ME not only ruled his death a homicide, but she took the unusual step of saying that the “method” was a police chokehold, experts and insiders say.

That would require hard proof, starting with sophisticated medical evidence in the neck of specific broken bones and damaged tissue, and ending with certainty that Pantaleo used a chokehold barred by the NYPD.

The 29-year-old officer waived immunity and took the stand for two hours, insisting he used an authorized NYPD takedown tactic on Garner — and not a chokehold.

In addition, NYPD trainers and the department's records on takedown techniques were also introduced, and their testimony did not refute Pantaleo, sources said.

In addition, the ME’s report also stipulated that a host of medical maladies contributed to Garner’s demise — he was obese, had heart disease, high blood pressure and was asthmatic, and chest compression during the struggle further stressed his body.

A spokesman for the Medical Examiner's office declined comment.

Lastly, there was questionable work of paramedics from Richmond County Hospital, who were captured on video doing virtually nothing to help the ailing Garner, suggesting that their inaction contributed to Garner's death.

Despite these obstacles, Donovan’s prosecutors believed they had made a strong presentation that warranted a charge.

"They thought they had made the case to go to trial," a source said.

A federal civil rights investigation has been launched into Garner’s death, as well as a separate NYPD Internal Affairs probe to determine if Pantaleo violated department guidelines.

Those inquiries could take months.