New York City police and environmental protection officials isolated and removed the suspicious letter, and testing “determined there was no dangerous substance,” Bragg spokesperson Danielle Filson said. The substance was sent to a city lab for further examination, police said.

“Alvin, I am going to kill you,” the letter said, according to a person familiar with the matter. The person was not authorized to speak publicly about an ongoing investigation and did so on condition of anonymity.

The discovery, in the same building where a grand jury is expected to resume work Monday, came amid increasingly hostile rhetoric from Trump, a Republican who is holding the first rally of his 2024 presidential campaign Saturday in Waco, Texas.

Hours earlier, Trump posted on his Truth Social platform that any criminal charge against him could lead to “potential death & destruction.”

Trump also posted a photo of himself holding a baseball bat next to a picture of Bragg, a Democrat. On Thursday, Trump referred to Bragg, Manhattan’s first Black district attorney, as an “animal.”

The building where the letter was found wasn’t evacuated and business mostly went on as usual, with prosecutors coming and going and bicycle delivery workers dropping off lunch orders. The building houses various government offices, including the city’s marriage bureau.

Security has been heavy around the court buildings and district attorney’s office in recent days as the grand jury investigates hush money paid on Trump’s behalf during his 2016 campaign.

Additional police officers are on patrol, metal barricades have been installed along the sidewalks and bomb sniffing dogs have been making regular sweeps of the buildings, which have also faced unfounded bomb threats in recent days.

A New York State court spokesman said, “Due to the nature of increased interest in proceedings in New York City Courthouses, we have increased security, both inside and on the perimeter, and officers have been reminded to remain vigilant and maintain situational awareness.”

In a memo to staff Friday, Bragg said the office has also been receiving offensive and threatening phone calls and emails. He thanked his staff of nearly 1,600 people for persevering in the face of “additional press attention and security around our office“ and said their safety remains the top priority.

“We will continue to apply the law evenly and fairly, which is what each of you does every single day,” Bragg wrote.

The Rev. Al Sharpton said he will hold a prayer vigil for Bragg’s safety Saturday in Harlem. He and other Black leaders have condemned Trump’s rhetoric about Bragg and billionaire George Soros, who backed a group that supported Bragg’s campaign, as “not a dog-whistle but a bullhorn of incendiary and anti-semitic bile.”

The grand jury, convened by Bragg in January, has been investigating Trump’s involvement in a $130,000 payment made in 2016 to porn actor Stormy Daniels to keep her from going public about a sexual encounter she said she had with Trump years earlier. Trump has denied the claim.

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Associated Press writer Bobby Caina Calvan contributed to this report.