NEW YORK CITY — A grand jury chose not to indict the cop who killed unarmed National Guardsman Noel Polanco during a traffic stop in Queens last year — dealing a blow to the dead man's family, sources said.

According to a source, the fact that Detective Hassan Hamdy only fired a single shot during the incident last year worked in his favor in the decision.

Hamdy shot Polanco, 22, after he was pulled over on the Grand Central Parkway on Oct. 4, 2012. Sources said that Hamdy believed Polanco was reaching for a gun when he opened fire.

Sanford Rubenstein, the lawyer for Polanco's mom, Cecilia Reyes, said he was disappointed with the vote.

"The family of Noel Polanco is extraordinarily disappointed the Queens grand jury did not vote to indict the police officer who shot and killed him," he said in a statement.

Detective Hassan Hamdy seen here outside his Long Island home. View Full Caption Victor Alcorn/Splash News

"The family will in the near future meet with their advisors to determine the best way to move forward in their quest for justice."

Rubenstein said Friday that he would seek civil action and push for the U.S. Attorney's office to intervene. The family also plans to hold a rally Saturday morning in Harlem.

According to Queens District Attorney Richard Brown, the grand jury met nine times during a five-week period.

"Suffice it to say, however, that this office conducted a thorough, complete and independent investigation into all of the facts and circumstances surrounding Mr. Polanco’s death," Brown said in a statement.

"Mr. Polanco’s death remains a tragedy and I again express my sympathy to his family for their loss."

Hamdy's attorney, meanwhile, said the detective was happy not to be charged, but remained broken up about the incident.

"Detective Hamdy is extremely relieved by [Thursday's] decision," said Phil Karasyk, the attorney representing the cop. "This is something that he never wanted to have happen.

"No police officer ever wants to be faced with such a life-or-death, split-second decision," he added. "It stays with them forever. He once again extends his sincere condolences to the Polanco family."

Polanco served in the Army National Guard and was looking forward to going into the active military and eventually becoming a cop.

The night of the shooting, Polanco went to Ice Lounge, in Astoria, and picked up a friend who bartended there, Diane DiFerrari, as well as Vanessa Rodriguez, an off-duty NYPD cop.

On the way back to LeFrak City, cops spotted Polanco driving his Honda erratically around 5:15 a.m.

During the pursuit, Polanco weaved in and out of police vehicles and nearly hit a van that was carrying Emergency Services Unit officers.

After cops boxed him in around 94th Street, Hamdy approached the car and shouted "Police, let me see your hands!"

Police said that Polanco reached under the seat at that point and Hamdy let off a single shot, killing him. No weapon was found.

But DiFerrari told investigators that Polanco's hands were on the steering wheel the whole time.

At her home Thursday afternoon, DiFerrari appeared shocked when told Hamdy was not indicted.

"He wasn't indicted?" she said, covering her face with her hands.

During grand jury testimony, Hamdy choked up and said that "the last thing I ever wanted to do was take a life," sources said.

Additional reporting by Paul DeBenedetto