Police Commissioner Bill Bratton is calling Thursday's hatchet attack on two police officers on patrol in Jamaica an act of terror.
Zale Thompson, 32, was shot and killed by police after he hit the officers with an 18-inch metal hatchet.
Officer Kenneth Healey, 25, was struck in the back of the head, and remains hospitalized with a skull fracture in critical but stable condition.
During a Friday press conference, Bratton and other police officials said they believe Thompson's attack on the officers, who were posing for a photographer, was premeditated, and that he acted alone.
An investigation has found Thompson was discharged from the U.S. Navy and convicted of domestic assault in California. He recently visited websites associated with terror groups such as ISIS and Al Qaeda.
Police also said Thompson had viewed videos of beheadings.
"This is something he has been thinking about for some time, and thinking about with more intensity in recent days," NYPD Deputy Commissioner John Miller said.
Metro previously reported the four officers involved in the incident had graduated from the police academy earlier this year.
Another officer was hit in the arm with a hatchet, and a bystander was hit in the back from a stray police bullet.