NYPD Officer Brian Moore, a native son of Massapequa, died Monday, two days after police said he was shot in the head in Queens by a felon investigators suspect used a five-shot revolver stolen from a Georgia bait and tackle store.

Moore, 25, a graduate of Plainedge High School in North Massapequa who still lived on the street where he grew up, had been on life support with no brain activity at Jamaica Hospital Medical Center since Saturday's shooting, a source said.

Earlier Monday, Queens District Attorney Richard A. Brown said he would seek to charge Demetrius Blackwell, 35, of 104-25 212th Place, Queens Village, with first-degree murder, which carries a penalty of life in prison without the possibility of parole.

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Blackwell was arrested about 90 minutes after authorities said he gunned down Moore, just after 6 p.m. Saturday night.

Before Moore's death, Blackwell faced two counts of attempted first-degree murder and assault and weapons charges at his arraignment Sunday in a Queens courtroom packed with NYPD officers.

Monday night at a news conference at NYPD headquarters, Chief of Detectives Robert Boyce said investigators recovered a Taurus model 85 revolver in a backyard not far from where the shooting took place in Queens Village.

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The handgun was found underneath a box near a barbecue grill, Boyce said.

Investigators have traced the weapon to a Georgia bait and tackle shop, where it was among 23 firearms stolen on Oct. 3, 2011, Boyce said.

Nine of those guns have made their way to New York City, he said.

Mayor Bill de Blasio said at the news conference, "Our city is in mourning, our hearts are heavy. We lost one of New York's Finest. We lost one of the best among us."

Earlier in the day, Police Commissioner William Bratton gave the news at the Jamaica hospital that Moore had died.

"It is with great regret and sadness that I announce the passing of New York City Police Officer Brian Moore, shield No. 469, New York City police officer, hero of the city, killed in the line of duty," Bratton said. "In his very brief career, less than five years, he had already proved himself to be an exceptional young officer."

Bratton noted that Moore had made more than 150 arrests and received two exceptional service medals and two meritorious service medals.

Hundreds of officers -- among them those from the 105th Precinct in Queens where Moore worked -- stood in formation outside the hospital as his body was removed, placed into an NYPD ambulance and transported to Manhattan for an autopsy. Bratton noted last night that as the ambulance traveled through the city past several FDNY stations, firefighters stood at attention and offered a solemn salute.

Moore's weeping family members -- who stood amid the hospital processional -- were brought home under heavy police protection. His father and uncle retired as NYPD sergeants. Moore also has cousins who are officers with the NYPD, as well others who serve in East End police departments, officials said.

Two witnesses have identified Blackwell as Moore's killer, Boyce said, adding the suspected gunman was captured on video after the shooting. Boyce would not say what the video showed.

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He said Blackwell has a lengthy criminal record that started when he was 15.

Blackwell served 5 years in prison for attempted murder and was released from upstate Clinton Correctional Facility in 2008, according to prison records.

The officer was working plainclothes on an anti-crime initiative Saturday night at the time of the shooting, police said. He was driving an unmarked car with his partner, Erik Jansen, 30, when they encountered Blackwell at about 6:15 p.m. near the intersection of 212th Street and 104th Road in Queens Village, authorities said.

Moore and Jansen saw Blackwell tugging at his waist and sensing he had a gun, asked him: "What are you carrying?"

Blackwell, authorities said, immediately fired three shots. The recovered gun had three spent rounds and two live rounds in the chamber, Boyce said.

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Jansen radioed for help and officers raced Moore to the hospital. Jansen later identified Blackwell as the shooter at the 105th Precinct and two eyewitnesses told police they saw Blackwell running from the scene.

NYPD Patrolmen's Benevolent Association president Patrick Lynch said Moore's family "is devastated. There's no closure for a New York City police officer's family in death."

Nassau County officials, including the police department and County Executive Edward Mangano, also issued statements offering their condolences to Moore's family.

A wake will be held for Moore Thursday, followed by a funeral on Friday, Bratton said.

President Barack Obama, at an unrelated event at Lehman College in the Bronx Monday, said Moore and other officers "in the NYPD and across the country deserve our gratitude and our prayers, not just today, but every day. They've got a tough job."

Outside the family home, Nassau police officers stood guard Monday while neighbors hung blue ribbons in Moore's honor. Flags in Nassau County and at NYPD police headquarters in lower Manhattan were lowered to half-staff.

Moore's killing is the third line-of-duty death of an NYPD officer in the past five months. Two other city officers have been shot in that time, but survived.

Blackwell's court-appointed defense attorney, David Bart, of Flushing, Queens, said Tuesday morning he had not spoken to his client since Sunday's arraignment. He said any comment on the Queens district attorney's plans to seek an indictment Tuesday before a grand jury on upgraded charges of first-degree murder would be "premature." 

Bart also declined to comment on a handgun found near the scene of the shooting that police believe Blackwell used to shoot Moore. 

"At this point, I can't comment on the gun at all," he said, adding that he would seek any forensics evidence. 

Bart called the officer's passing "tragic" and added: "From everything I've heard about the officer, he was a fine young man." 

With Alison Fox and Emily Ngo