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How Puerto Rico's death toll climbed from 64 to 2,975 in Hurricane Maria

(CNN) Puerto Rico's true death toll from Hurricane Maria remains elusive as the storm's one-year anniversary approaches.

The island government raised the official death toll to 2,975 on Tuesday after maintaining for months that 64 people had died as a result of the storm.

But the higher figure, based on the findings of researchers from George Washington University in a study commissioned by the US commonwealth's government, is only an approximation, not a concrete list of names, according to Gov. Ricardo Rossello.

"This number can change," Rossello said. "It could be less, it could be more, as time passes."

Here's how the official death toll has changed since the storm touched down September 20 as a Category 4 hurricane:

6 to 13 deaths

In the chaos after the storm, the island's public safety director, Héctor M. Pesquera, said at least six people were killed.

Rossello told CNN two days after the storm hit that 13 people had died in the storm. That figure was based on reports from mayors on the island, but law enforcement authorities hadn't confirmed the total, the government said.

Death toll rises to 34

Nearly two weeks after Maria, President Donald Trump touched down for the first time and downplayed the devastation.

"Every death is a horror," Trump said in early October before comparing Puerto Rico's official death toll of 16 at the time to "a real catastrophe, like Katrina," in which more than 1,800 people perished from the 2005 storm that ravaged New Orleans.

After Trump departed, the governor announced the death toll had risen to 34.

One of the conclusions of the George Washington University study was that officials did nothing to respond to public criticism and concerns about political motivations that surged when the official tally jumped to 34 shortly after Trump's visit.

Funeral homes identify nearly 500 hurricane-related deaths

In November, CNN reporters surveyed 112 funeral homes across the island, about half the total. They found that funeral home directors identified 499 deaths considered to be hurricane-related.

Official toll climbs to 64

In December, public safety officials revised the official count to 64, adding some fatalities newly certified as indirect deaths related to the storm.

For instance, emergency personnel were unable to reach the home of a man who collapsed during the storm. Doctors had classified his death as natural, and it was not initially considered a storm-related death.

Other deaths later determined to be indirectly caused by the storm included a case of exposure to carbon monoxide, a suicide, a person run over by his own vehicle and a death from complications following a fall.

Estimated 1,052 'excess deaths' after Maria

Also in December, The New York Times estimated 1,052 "excess deaths" occurred after Maria. Other media produced similar estimates.

Estimate of 4,645 deaths become rallying cry

In May, a team that included researchers from Harvard University published a study in the New England Journal of Medicine estimating 793 to 8,498 people died in Maria's wake, a range that some academics have criticized as overly broad.

The study's midpoint estimate -- 4,645 deaths -- became a rallying cry for activists upset by what they see as a lack of accountability for the scale of the catastrophe by officials in Puerto Rico and the United States.

An estimated 1,006 to 1,272 deaths

A research letter published this month in the medical journal JAMA estimated that between 1,006 and 1,272 people died in connection to the storm.

Puerto Rican government admits to 1,427 more deaths than 'normal'

The Puerto Rican government on August 8 quietly admitted the official toll was higher than its December tally.

In a report to Congress, the government said documents show that 1,427 more deaths occurred in the four months after the storm than "normal," compared with deaths that occurred the previous four years.

The 1,427 figure also appeared in a draft of the report -- "Transformation and Innovation in the Wake of Devastation" -- which was published and opened for public comment July 9.

The revised figure was first "revealed" by the Puerto Rico government, according to the final report, on June 13, one day after officials were forced by a judge to release death records that CNN and the Centro de Periodismo Investigativo in Puerto Rico had sued to make public.

But officials at the time stopped short of updating the official death toll.

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