New York City has launched a review of how accused "subway ripper" Rigoberto Lopez slipped through the cracks of Mayor Bill de Blasio’s social and mental welfare bureaucracy in the aftermath of an A-train slashing spree that left two dead and two others injured, Hizzoner said Wednesday.

Lopez was arrested at least four times in recent years before the attacks, and police officials have said he was suffering from mental distress in two of those cases. Additionally, Lopez’s family claims the 21-year-old was seeing a social worker before the coronavirus pandemic stopped the visits.

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"The initial information that we have received suggests that the situation did not sound the kind of alarms that we have seen in some other cases, where someone was clearly diagnosed with a mental health issue — not just indicated by an individual officer, but diagnosed with a mental health issue or had a history of a specific violent act," de Blasio said when pressed by The Post Wednesday at his daily briefing.

"Those situations are supposed to set off specific alarms with specific follow-through actions," he added. "I’m waiting for the full results of the review of what happened in this case. But, the last report I had was we did not have that kind of specificity in his situation."

Rigoberto Lopez was arrested at least four times in recent years before the attacks, and police officials have said he was suffering from mental distress in two of those cases (FILE)

Lopez — who lived in a Brooklyn homeless shelter — was arrested by the NYPD still wearing clothes stained with blood and in possession of a knife after his alleged role in brutal and deadly stabbing attacks along the A train’s three-borough route, which shook the city.

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The two people killed in the four attacks, which unfolded over a 24-hour period between Friday and Saturday mornings, were also both homeless.

"What happened here was horrible and we’ve got to learn from every situation," de Blasio told reporters. "We’ve got to constantly refine the ability of different agencies to work together."

Those stabbings were the latest in a string of attacks on New York City’s subway system, which has seen key violent crime metrics surge or remain flat even as ridership plunged amid the coronavirus pandemic.

MTA officials have demanded the city provide an additional 1,000 cops to patrol the system after City Hall agreed to their initial request to bump up patrol strength underground by roughly 500 officers in the immediate aftermath of the killings.

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