Seventeen hours after an NYPD police officer was shot and killed in East Harlem, Mayor Bill de Blasio called on the criminal justice system to do more to protect its citizens and police officers.

Police said Tyrone Howard, 30, shot Officer Randolph Holder in the forehead Tuesday night on an FDR overpass. At a 1 p.m. press conference at Harlem Hospital, de Blasio said Howard, who has not yet been formally charged, was "obviously a hardened, violent criminal" and more needs to be done to ensure people like him are not on city streets.

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De Blasio spoke of the "unrelenting flow of illegal fire arms" in the city and said so often it is the city's police officers who pay the price — officers like Holder, a third generation cop.

"He represents the best of society," de Blasio said. "He represents the immigrant tradition of trying to make this place better for everyone, and he made the ultimate sacrifice."

Holder and another officer approached Howard on suspicion he was connected to a bicycle theft earlier in the night. Police said Howard immediately drew a gun and shot Holder in the head when he saw the officers approaching. Howard was arrested on 125th Street after fleeing the scene of the shooting.

Police Commissioner Bill Bratton said funeral arrangements for Holder were not yet finalized. An update on those services was expected Wednesday afternoon.

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Investigators said they were combing through extensive video and physical evidence, and that the investigation was far from over.

"Some things we have been able to nail down, but others are in motion as the investigation goes forward," Bratton said.