NEW YORK CITY -- An "unprovoked" machete attack on three New York City police officers near Times Square on New Year's Eve is being investigated as a possible terrorist incident. The suspect is a 19-year-old man from Maine, whose online posts indicate recent Islamic radicalization, sources told ABC News.
Investigators are looking into whether the suspect came to the annual ball drop specifically to wage an attack on law enforcement, the sources said.
The incident occurred just after 10 p.m. on Saturday near West 52nd Street and 8th Avenue, outside the secure area that had been set up for New Year's Eve celebrations, Police Commissioner Keechant Sewell told reporters at a news conference at Manhattan's Bellevue Hospital.
"Unprovoked, a 19-year-old male approached an officer and attempted to strike him over the head with a machete," Sewell said. "The male then struck two additional officers in the head with the machete."
One of the officers fired their weapon, striking the suspect in the shoulder, Sewell said. The suspect was taken into custody, she said.
The suspect was identified as Trevor Bickford of Wells, Maine Monday morning.
He's been charged with attempted murder of a police officer and attempted assault.
The three injured officers were taken to Bellevue, Sewell said. All three officers were released from the hospital on Sunday.
Bickford remained hospitalized at Bellevue Monday.
Suspect relatives reported concerns
While a motive remains under investigation, authorities are not ruling out the possibility that the suspect came to New York City specifically to attack police officers at the Times Square ball drop, law enforcement sources told ABC News.
Multiple law enforcement sources identified the suspect as Trevor Bickford, 19, of Wells, Maine. He took an Amtrak train to New York City on Dec. 29, the sources said.
Federal and local law enforcement investigators are combing through the suspect's online postings, which indicate recent extremist Islamic radicalization, the sources said.
Bickford has no prior arrests. His mother and aunt notified law enforcement in recent weeks about their concerns he was gravitating toward dangerous Islamist ideologies, the sources said. The report prompted the FBI's Joint Terrorism Task Force to look into the suspect, the law enforcement sources said.
The NYPD counterterrorism bureau is investigating the New Year's Eve attack in conjunction with the FBI.
Should authorities determine the attack was motivated by an Islamist ideology, it would make it the first terror incident associated with New Year's Eve in Times Square, authorities said.
Prior to New Year's Eve, the NYPD noted in a pre-event assessment that throughout December "multiple pro-ISIS users disseminated extremist propaganda graphics broadly calling for attacks in advance of the New Year, advocating a wide range of low-tech tactics." Islamist terror groups have long promoted knife attacks.
Both federal and local law enforcement stressed at Sunday morning's news conference the attack appeared to be an isolated incident and there was no longer a threat.
Injured officers in stable condition
One of the injured officers, an eight-year veteran of the NYPD, suffered a laceration to the head, officials said. Another hurt officer had just graduated from the police academy on Friday, and as is traditionally the case, his first assignment was the New Year's Eve detail in Times Square. The rookie officer was also struck in the head, resulting in a skull fracture and large laceration, officials said.
"We are really pleased by the response and how our officers handled this situation," Mayor Eric Adams said. "All three of the officers are in stable conditions and there are no critical threats to New Yorkers at this time."
FBI Assistant Director in Charge Mike Driscoll said the bureau's Joint Terrorism Task Force is involved to "ascertain what is the nature of the attack." He said that the FBI believes the attacker was acting alone.
The NYPD released an image of a weapon, saying it had been recovered at the scene. The weapon appeared to be a Gurkha knife, a type of curved blade, according to ABC News contributor Darrell M. Blocker, a retired CIA operative.
Patrick Lynch, president of the Police Benevolent Association of the City of New York, said, "Let's think about those family members here who are in shock right now, never thinking the first call of the year would be their son, their husband, their family member would be here in Bellevue Hospital."
Videos from the scene appeared to show revelers jogging through the rain as they were directed away from the scene by columns of police officers.
David Lyugovski, of California, told ABC News that he saw dozens of officers, some with guns drawn, running toward the scene of the incident.
"They're all telling us to go towards the viewing area for the ball drop and everybody's running, everybody's panicking," Lyugovski said.
Lyugovski and his brother-in-law, Andrew Dyachkin, of South Carolina, were in New York to watch the Times Square ball drop, they said in a joint video interview.
"Somebody's yelling, 'Calm down, calm down,' because everybody's on edge," Dyachkin said. "Like, I'm sure in the back of all of our minds, now this could be a target for, you know, shooting."
He added, "We thought someone is trying to shoot, you know, as many people as possible. Another mass shooting."
One of the officers involved in the incident had graduated from the police academy on Friday, Sewell said.
Adams spoke at the officer's graduation ceremony, he said.
"It just goes to show you, it could be your first day or it could be your last day, the actions that police officers must take every day are life-threatening situations," Adams said.
ABC News' Josh Margolin, Keith Harden, Patricio Chile and Mark Crudele contributed to this report.