NEW YORK (CBSNewYork) — Officials said Sunday that Dr. Henry Bello, the gunman who opened fire at Bronx-Lebanon Hospital Center last week and shot seven people, had worked recently for the City of New York.

Sources said Bello was hired by the city’s Human Resources Administration, according to City Hall spokeswoman Jaclyn Rothenberg. Sources said he had been a probationary caseworker with the HIV/AIDS Service Administration and was hired in September 2016.

He had also previously worked for the city Health and Hospitals Corporation, Rothenberg said.

Bello was subjected to a criminal background check, but his prior 2004 arrest did not appear in the check because he had pleaded guilty to a lower charge that didn’t show up as a disqualifying offense in a background check, Rothenberg said.

Sources told CBS2 that Bello had been arrested several times, including the 2004 arrest for sexual abuse.

As CBS2’s Hazel Sanchez reported, Bello stopped coming to work on April 11 of this year, and after several attempts to contact him – including through his union – Bello was terminated on June 21, sources said.

Bello sneaked an AM-15 assault rifle under a white lab coat to the 16th floor and shot seven people before fatally shooting himself at the hospital Friday afternoon, according to police.

Dr. Tracy Tam, 32, of Jamaica, Queens, was killed in the shooting.

Doctor Killed In Bronx-Lebanon Hospital Center Shooting Identified As Jamaica, Queens Woman

Sources told CBS2 that Tam was supposed to be off onF riday.

Tam had graduated from residency exactly one year before her death.

“It was very unfortunate that you know, that the tragedy happened to her because she was such a nice person,” coworker Marc Duplessy told CBS2.

One of Tam’s coworkers has set up a GoFundMe account for her family.

“She was a genuine and compassionate person, and really just love and understanding, and just broke all of hearts to hear what happened to her,” said Jason Rugel, a friend of Tam’s.

Officials said earlier Bello resigned from Bronx-Lebanon in 2015 amid sexual harassment allegations.

Some coworkers remember Bello threatening to kill people after he left in 2015, but the hospital claims it was never notified.

“We’re not aware of any such reports,” said hospital spokesman Errol Schneer.

Sources also said Sunday that the assault rifle Bello used was legally purchased in a gun shop in upstate Schenectady.

Officials say all but one of the victims in the shooting were hospital employees. Dr. Tam had graduated from residency exactly one year before her death.

The six people wounded in the shooting remained hospitalized Sunday.