A Queens lawmaker accused the head of first lady Chirlane McCray’s embattled “ThriveNYC” mental health initiative of refusing to explain why the city ignored so many warning signs surrounding the vagrant who bludgeoned four homeless men to death in Chinatown last weekend – because she has no answers.

Councilman Robert Holden (D-Queens) initially called out ThriveNYC Director Susan Herman and other city officials during a council hearing Tuesday. He was asking them how Randy Santos, 24, went under the city’s radar despite having a history of unprovoked violence – including a November arrest for allegedly biting a man on the chest.

“There were certainly a number of red flags over the years,” Holden said. “There was a trail of violence all involving random people.”

“These signs were here with this individual for years, and he was in and out of the system,” added Holden. “This is again happening all over the city – random attacks. Does this kind of thing red flag your agencies at all to say ‘we should step in’?”

Neither Herman nor Myla Harrison, assistant commissioner for the Department of Health, directly answered his questions during the hearing on mental health services for immigrants.

Instead, they tried to shift focus by insisting most homeless New Yorkers don’t suffer from mental illness and that they’re limited from discussing Santos’ treatment history.

“We were all horrified by what happened, and we are all looking at it, and we will learn from this incident, “ Herman said. “[But] I think you are aware of the fact that we can’t talk about specific services this particular individual accessed [by law].”

Holden tried to ask follow-up questions but was cut off by Councilman Carlos Menchaca (D-Brooklyn), chairman of the immigration committee, who claimed he wanted to give other legislators the chance ask questions.

Holden left the hearing fuming and later accused Herman of “dodging” his questions, adding McCray’s $250 million Thrive initiative “lacks a real plan to deal” with emotionally disturbed persons like Santos.

“[Herman] could have said, ‘I can’t speak about this case, but hypothetically we do this when this happens,’” Holden said. “But she didn’t want to because she couldn’t — and that’s the whole thing.”

“They are not helping the seriously mentally ill,” he added. “The city is not doing its job with all the money they are putting towards ThriveNYC.”

Thrive spokesman Joshua Goodman said Wednesday that “confidentiality law on social services and health care prevent us from talking about what kinds of services any individual has received, and that’s true even after a horrifying tragedy like this.”

He added the city has “community engagement and crisis response teams and psychiatrists and clinicians activated in the [Chinatown] community to help people deal with the trauma of this tragic event, and we also want to make sure every city agency is doing all it can to prevent such violence.”

McCray was not at Tuesday’s hearing but hours earlier insisted during a NY1 interview that “Thrive is a success” because its very existence is spurring more discussions about mental health.

McCray — who has come under fire from city officials for a lack of data to explain her program’s hefty price tag — also insisted that teams of social workers and therapists would never have been deployed to help the homeless in Chinatown if it weren’t for her.