There was something fishy about the invoice: why was a company in Singapore billing Brazil $45 million for an Indian Covid-19 vaccine that hadn't been delivered?
The request for payment for three million doses of Indian firm Bharat Biotech's Covaxin vaccine landed on March 18 on the desk of Luis Ricardo Miranda, head of medical imports at the Brazilian health ministry.
There were several red flags, according to Miranda, who testified Friday before a Senate panel investigating the government's handling of the pandemic, which has claimed more than 500,000 lives in Brazil, second only to the United States.
It was peculiar Brazil was buying Covaxin at all, given that far-right President Jair Bolsonaro -- who regularly flouts expert advice on Covid-19 -- had previously rebuffed offers of cheaper, more effective vaccines.
But what worried Miranda was that Brazil's $300 million contract for Covaxin made no mention of the firm that sent the invoice, Madison Biotech, an apparent shell company.
Also, the vaccine had not arrived -- and did not even have regulatory approval in Brazil.
- 'Excessive' pressure -
Yet Miranda started receiving phone calls at all hours from his bosses, putting what he called "atypical, excessive" pressure on him to approve the payment.
Other irregularities in Brazil's Covaxin deal soon emerged, forcing the administration to cancel it as prosecutors opened an investigation.
According to newspaper Estado de Sao Paulo, Bharat Biotech initially quoted a price of $1.34 a dose.
But Brazil agreed to pay $15 a dose, more than any other vaccine it purchased.
Miranda took his concerns to his brother, Congressman Luis Miranda, a Bolsonaro supporter.
Congressman Miranda went to the president -- who is now in the hot seat over accusations the Covaxin deal was a front to embezzle millions of dollars, that a key ally masterminded the plan, and that Bolsonaro knew all about it.
The scandal risks exploding: the Senate commission is now set to vote on whether to formally accuse the president of malfeasance, and opponents have called anti-Bolsonaro protests for Wednesday and Saturday.
- The plot thickens -
The Miranda brothers say they met with Bolsonaro on March 20 to warn him the Covaxin contract could be a dirty deal.
"The president looked me in the eye and said, 'This is serious,'" testified Congressman Miranda.
"'If I interfere with this thing, you know what kind of shit it's going to stir up. This must be So-and-So's deal,'" he said the president told him.
Pressed by senators to identify "So-and-So," the congressman insisted he could not remember.
Then, on the verge of tears at the end of a marathon hearing, he caved.
"I'm going to be persecuted. I've already lost everything. I know what's going to happen to me," said Miranda, who arrived at the session in a bulletproof vest.
But he coughed up the name: Ricardo Barros, a powerful congressman who is head of Bolsonaro's coalition in the lower house.
- 'First big bomb' -
Barros, a former health minister, denied wrongdoing, as did Bolsonaro, who accused the Miranda brothers of a smear campaign.
But the scandal could be devastating, at a time when Bolsonaro's support is dwindling and polls place him far behind leftist ex-president Luiz Inacio Lula da Silva in elections next year.
"It was the first big bomb" to come from the two-month-old Senate inquiry, said Geraldo Monteiro, a political scientist at Rio de Janeiro State University.
"We'd had testimony showing the government's negligence and denialism, but nothing really serious that could potentially lead to impeaching the president," he told AFP.
Now, Brazil's shortage-plagued vaccination campaign and the lives it has cost look not just inept, but potentially criminal -- with the president himself accused of wrongdoing.
If senators formally accuse Bolsonaro of malfeasance for failing to have Barros investigated, he could theoretically be tried in the Supreme Court and removed from office -- though it looks unlikely that Prosecutor General Augusto Aras, an ally, would bring charges.
The more immediate problem for the president is Barros.
Protect him, and Bolsonaro wrecks the anti-corruption platform that helped him win the presidency in 2018. Ditch him, and he risks shattering his alliance with Barros's "Centrao" coalition.
Bolsonaro has a fragile marriage of convenience with the Centrao, a loose group of parties known for their knack for gaining access to government pork.
The alliance has notably protected the polarizing president from facing the more than 100 impeachment cases opponents have brought against him in Congress.
The gatekeeper to open impeachment proceedings is the speaker of the lower house, Arthur Lira.
Both Lira and Barros belong to the Progressives Party (PP), a key player in the Centrao.
"Barros could start pressuring his party to break with Bolsonaro. At a time when Bolsonaro is losing popularity and the impeachment push is gaining momentum, he needs the PP more than ever to stay alive," said public-law expert Michael Mohallem.
It is still early days, and far from certain "CovaxinGate" could fell the president, who points out Brazil never bought the vaccine in the end.
But the threat is in the air -- and in a joke that went viral on social media: "Covaxin is so strong it's going to bring down Bolsonaro."