Mayor Bill de Blasio said Wednesday that the man suspected of fatally shooting NYPD Officer Randolph Holder is a "hardened, violent criminal who should not be on the streets."

Police on Wednesday named Tyrone Howard, 30, as the suspect in the slaying of the officer and he is expected to be charged.

Police Commissioner William Bratton said that despite a life of "escalation of crime" Howard was out of jail on a diversion program.

"If ever there was a candidate not to be diverted, it was this guy," Bratton said. "He's a poster boy for not being diverted."

De Blasio said he didn't know the details of how Holder's case was handled by the judge "but I do know that he shouldn't have been on the streets."

Deputy Chief James P. O'Neill said Howard had been wanted in a gang-related shooting on Sept. 1. Police had made "numerous attempts" to arrest him, O'Neill said.

"We were hunting him, but it was obviously unsuccessful," O'Neill said.

The Associated Press reported that Howard had been arrested 28 times since he was 13 years old for offenses including drug possession and robbery, authorities said. He's been sentenced to state prison twice since 2007 on drug possession and sale convictions, state records show.

Howard was arrested in connection with a June 2009 shooting that left an 11-year-old with a gunshot wound to the leg and a 78-year-old grazed by a bullet, according to police.

The chief of detectives for Manhattan, William Aubry, laid out some of the details that police have learned so far about the police officer's shooting, telling reporters at a news conference: "I'm going to take you through the 13 minutes which led up to the death of Police Officer Holder."

As de Blasio and Bratton stood in the background, Aubry said that about 2:30 a.m. Tuesday, there were two housing officers on the roof of 420 E. 102nd St., and "they hear and they see individuals firing weapons at each other."

The men used at least three weapons, Aubry said. Howard was one of the men, and he fled northward on a promenade that runs between the FDR Drive and the East River, Aubry said.

At 106th Street, Howard stole a bicycle from a man at gunpoint and continued north, the chief said. Meanwhile, Holder and his partner, both in plainclothes, had been following three men across a walkway over the drive at 120th Street, believing mistakenly that the men were part of the group that had exchanged gunfire, Aubry said.

As Holder and his partner walked down the ramp on the promenade side, they encountered Howard heading north on the stolen bicycle, Aubry said.

"When Tyrone approaches them on the bicycle, he puts the bike down, he pulls out his weapon and he fires one time, striking the officer [Holder] in the front of the head," Aubry said. Howard then approached Holder's partner, who fired once, the chief said.

Howard fled north on the promenade, where he was arrested by other officers between 124th and 125th streets, Aubry said.

Holder, 33, a Brooklyn resident, was the fourth NYPD officer killed in the line of duty in less than a year.

Howard, who was wounded in the leg and treated at a hospital, is now being held at the 25th Precinct in East Harlem and would be put in lineups to determine whether he can be identified as the man who stole the bicycle and as one of the men who had exchanged gunfire, Aubry said. The chief said detectives would then consult with prosecutors about a murder charge in the slaying of Holder.

Bratton said Tuesday night that Holder had been on the force five years and was assigned to the housing bureau. He was pronounced dead at 10:22 p.m. at Harlem Hospital Center, Bratton said. Holder lived in Brooklyn, an NYPD spokesman said.

Bratton said Holder, a native of Guyana who was unmarried, joined the NYPD in 2010 and came from a law enforcement family. His father and grandfather worked as police officers in Guyana, Bratton said.

De Blasio said flags on city buildings and on stationary poles would be flown at half-staff until the day after Holder's interment.

The New York City Patrolmen's Benevolent Association president asked New Yorkers to remember Holder and his family.

"We ask all New Yorkers of good will to remember our fallen brother, Randolph Holder, and to keep his family, friends and colleagues in your heart, thoughts and prayers," Patrick Lynch said in a statement. "Randolph, like so many of his fellow officers before him, gave his life in the protection of the City he loved. Let his sacrifice mark a new day of respect and appreciation for the men and women who stand between violent crime and the good people of New York.

"Let his sacrifice mark a new understanding of what police officers do everyday and why we do it. And may his sacrifice bring us together in compassion and peace as we comfort those left behind and lay this hero to rest," Lynch said.

Gov. Andrew M. Cuomo held a moment of silence for Holder and his family before an unrelated event on the Upper East Side on Wednesday morning.

"They are in our thoughts and prayers and more, they have the support of every person in the state of New York," the governor said. "We hope that his family can find peace in this very difficult situation."

Cuomo called for stronger gun control legislation, saying gun violence has spiraled "out of control" in the city and the nation. Four NYPD officers killed in less than a year is one of the highest rates of police deaths in the nation, he said.

Cuomo mourned Holder as well as Carey Gabay, 43, a lawyer in his administration who was fatally shot hours before the West Indian Day Carnival Parade in Brooklyn last month. Gabay was a "beautiful, beautiful man" who was "just an innocent victim who happened to be in the wrong place at the wrong time," the governor said.

Holder's Brooklyn neighbors were shocked to hear the news of his death.

"Oh my God," Dawn Lundy, 46, said. Her mother put her hands over her mouth and gasped when Lundy told her.

Lundy said she heard about the shooting Tuesday night but didn't know that Holder was an officer.

Holder lived on the lower level of a two-story brick house, Lundy said. She saw him in passing and said he was among a cadre of helpful neighbors who would shovel one another's sidewalks.

"This is horrible," Lundy said.

She looked at the two patrol officers stationed outside Holder's home and said: "I don't know how you guys do this job."

Bratton said Holder was the fourth NYPD officer to be killed in the line of duty in less than a year. In May, NYPD Officer Brian Moore, 25, of Massapequa, was shot in the head as he and a partner patrolled in Queens Village. Moore died two days later, and Demetrius Blackwell, of Queens Village, was charged with the Plainedge High School graduate's killing.

Days before last Christmas, Officers Wenjian Liu, 32, and Rafael Ramos, 40, both of Brooklyn, were gunned down execution-style in Bedford-Stuyvesant, by a man who took his own life a short time later.

"Four police officers murdered in 11 months," Bratton said at the news conference. "That's about as bad as it gets."

With Anthony M. DeStefano and Darran Simon