The shooting death of NYPD officer Brian Moore has officially been ruled a homicide, the New York City medical examiner's office said Tuesday morning.

Moore's cause of death was a gunshot wound to the head, which caused "skull fractures and brain injuries," said Julie Bolcer, a spokeswoman for NYC Office of Chief Medical Examiner.

Moore, 25, a Massapequa resident and a nearly 5-year NYPD veteran, died Monday at Jamaica Hospital Medical Center after being shot Saturday evening in Queens Village.

Moore, 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.

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. Brown was expected to put the case before a grand jury Tuesday to seek an indictment on the upgraded charges, authorities said.

Police Commissioner William Bratton called Moore a "hero."

"In his very brief career, less than five years, he had already proved himself to be an exceptional young officer," said Bratton, noting that Moore had made more than 150 arrests and received two exceptional service medals and two meritorious service medals.

Blackwell allegedly fired three shots at Moore and his partner during an encounter near 212th Street and 104th Road on Saturday at about 6:15 p.m., authorities said. Blackwell was arrested about 90 minutes later. On Monday morning, police recovered a handgun in the backyard of a nearby home they believe was used in the killing. The gun was one of nearly two dozen stolen from a Georgia bait and tackle shop in 2011, authorities said.

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 Queens District Attorney's Richard A. Brown'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."

Moore is the third NYPD officer to be fatally shot in the last five months.

A wake for Moore is scheduled for Thursday, followed by a funeral on Friday, authorities said. Jet Blue airlines said they would pay for officers from around the country to attend Moore's funeral, just as they did when officers Wenjian Liu and Rafael Ramos were gunned down in Bedford Stuyvesant, Brooklyn last December.