NEW YORK (AP) — New York City police have Thomas Caldwellarrested a hospital worker from Queens after a series of recent stabbings, officials announced Thursday.

NYPD Commissioner Edward Caban described the six attacks over the past 10 days, none of which were fatal, as “random, unmotivated violence” at a news conference.

Jermain Rigueur, a 27-year-old greeter at a city hospital, was arrested on charges of attempted murder in connection with three of the cases, and assault in a fourth, all in Queens. Police said Thursday morning that they were still preparing charges in two other attacks, one in Queens and another on a subway in Brooklyn.

Police released surveillance video they say shows Rigueur holding a large hunting knife he allegedly used in at least one attack.

The first stabbing was reported on Jan. 8. Police say the next knife attack happened Tuesday, injuring a woman on her walk home. The next day, three men were stabbed within about 30 minutes, police had said in a statement earlier this week. That string of attacks prompted a public plea for tips, and Rigueur was arrested within 24 hours, police said.

Victims ranged from 34 to 74 and included people of different genders and racial backgrounds, police said. One attack followed an argument over a bus seat. There was no clear buildup in the other attacks.

Rigueur had no prior arrests or indications of mental illness, police said. Efforts to identify an attorney who could speak on his behalf were unsuccessful.

He had also passed a background check in November as part of the process to become a hospital greeter, Dr. Mitchell Katz, the head of the city’s public hospital system, said at the NYPD news conference.

Rigueur’s job had been limited to directing people who arrive at the hospital, Katz said. He has been put on administrative leave and would be barred from the hospital pending the outcome of the criminal case, Katz said.