New York may have undercounted Covid-19 deaths among its nursing home residents by thousands, according to a report by the state attorney general.
Letitia James says her inquiry revealed a dramatic discrepancy between reported deaths and the official tally.
It directly undercuts Governor Andrew Cuomo, who has boasted about his pandemic response.
If the findings hold true, it would mean over 13,000 nursing home deaths - the highest in the US.
The official tally - logged by the state's health department - currently stands at 8,711.
Mr Cuomo, a Democrat, has repeatedly defended his handling of nursing homes and argued that other states were doing far worse.
New York is one of the few states in the country that only counts nursing home deaths if they took place on nursing home property, leaving out residents who later died in hospitals.
In her report, Ms James, also a Democrat, found that "many nursing home residents died from Covid-19 in hospitals after being transferred from their nursing homes", which was not reflected in the health department's published numbers.
The 76-page report builds on nearly 1,000 complaints submitted by nursing home residents and their families since April. The findings are based on a survey of 62 nursing homes - about 10% of total such facilities in the state.
The attorney general's report also singled out Mr Cuomo's order in March last year as the virus peaked in his state that nursing homes should readmit residents who had tested positive for the coronavirus, in order to free up hospital space.
Ms James' report said further investigation would be needed to prove a link between that policy and the 4,000 or so nursing home residents who died after the guidance was issued.
But she said those admissions "may have contributed to increased risk of nursing home resident infection and subsequent fatalities".
Facing public outcry, Mr Cuomo repealed this policy after less than two months, but accepted no blame for the rise in nursing home deaths in the state. He also issued a much-criticised report that sought to defend his action.
The governor's directive was later scrubbed from the state department of health website, according to US media.
He tried to blame the policy on former President Donald Trump, but Politifact rated this claim mostly false.
New York Health Commissioner Dr Howard Zucker issued a 1,700-word statement downplaying the attorney general's findings.
The New York State Department of Health "does not disagree that the number of people transferred from a nursing home to a hospital is an important data point, and is in the midst of auditing this data from nursing homes," Dr Zucker said.
Mr Cuomo's office has not yet responded to the report, but he has taken a victory lap in recent months over his administration's fight against the virus.
Last autumn, he wrote a book touting his handling of the crisis, titled American Crisis: Leadership Lessons from the COVID-19 Pandemic.
In November, he received an Emmy award "in recognition of his leadership during the COVID-19 pandemic".
One of Mr Cuomo's most vocal public critics welcomed the attorney general's report.
Fox News meteorologist Janice Dean blames Mr Cuomo for her parents-in-law's deaths in separate New York nursing homes last year.
She told the channel: "Maybe the angels won. Maybe the angels will have their day in court and maybe this governor will be held accountable."