WASHINGTON (AP) — The last time Secret Service agents escorted a U.S. leader to face criminal charges, they kept their mission a secret — even from their own bosses.

It was Oct. 10, 1973, and just a few agents knew the history they would make in ensuring that Vice President Spiro Agnew appeared in a federal courtroom to enter a plea and resign from office.

"It was a big day for the country, and a sad day," said Jerry Parr, one of those agents, in a 2010 interview. "And we didn't tell anyone it was happening. For better and worse."

There is no secret the second time around: The Secret Service on Tuesday is expected to deliver former President Donald Trump to a New York City courtroom to be arraigned on state charges tied to hush money payments made in the weeks before the 2016 election. The event is sure to be a spectacle and Trump himself plans a news conference that evening.

While much has been made of Trump becoming the first former president to appear in court to answer an indictment, the Secret Service has been in a similar spot before. And there are lessons to be gleaned in how Parr and other agents helped Agnew navigate his final hours as the nation's 39th vice president.

The main one: The agents allowed their admiration of Agnew, who died in 1996, to get in the way of properly doing their jobs.

Parr, who joined the Secret Service in 1962, wasn't sure what to expect when he was tapped a decade later to be the deputy chief of Agnew's detail. The vice president had a reputation for being President Nixon's attack dog and skewering political opponents as "nattering nabobs of negativism," "vicars of vacillation" and "pusillanimous pussyfooters."

Behind closed doors, however, Parr discovered that Agnew was nothing like his antagonistic persona.

"He was actually a very nice man," said Parr in a series of interviews for a book on the agent's life-saving role in the Ronald Reagan assassination attempt. "All the agents really liked him."

An example of Agnew's kindness occurred in 1972 when the Parrs threw a Christmas party for agents. Agnew insisted on coming so agents working on that shift could attend. Not many top government officials were that thoughtful, according to Parr, who died in 2015 at 85.

"To a unique degree the vice president and his wife, Judy (whom we called 'Mrs. A'), recognized our humanity and appreciated our service," Parr wrote in his 2013 memoir, " In the Secret Service." "To them, we were people and not furniture that came with the job."

Signs of Agnew's serious legal trouble emerged in August 1973 when the U.S. Attorney for Maryland informed Agnew that prosecutors were investigating the vice president for allegedly taking bribes as Maryland's governor. It did not take long for news of the investigation to dominate front pages.

"Suffering showed on his now-haggard face," Parr wrote. "As summer passed into autumn, I frequently heard sighs and groans coming from the backseat of the car; sometimes the soft sound was Mrs. Agnew weeping as her husband tried to comfort her."

One morning, Parr said, the vice president grew upset when they drove past a platoon of journalists staking out his house in a tony Washington suburb. "They just want to put me in jail," Agnew huffed.

Parr turned in his seat and jokingly told Agnew not to worry: He would go to jail with him. "And we'll find someone to smuggle us a hacksaw blade in a pie," Parr added, "so we can get you out."

Within a few weeks, however, Parr's boss, Samuel Sulliman, pulled him aside to explain that Agnew would soon be entering a plea to end the investigation. As part of the deal, he would have to resign.

Parr's job would be to escort Agnew to the Baltimore federal courthouse. Sulliman warned his deputy that "he didn't know if we had to take him to jail after the (hearing), or not, and I should know that," Parr said. "The judge could sentence him to prison."

Next, Sulliman gave Parr an order: He could tell no one about the trip, not even their superiors.

Upon learning that the vice president might resign, the Secret Service would be required to rush agents to protect the House speaker, next-in-line for the presidency. Such a move would draw the attention of reporters. Agnew didn't want news to leak before his resignation became official, and he asked his detail to keep it quiet.

"I only knew about it because Sam told me, and Sam was sworn to secrecy," Parr said of his boss in a 2008 oral history. On Oct. 10, a warm Wednesday, the vice president's motorcade made a quick stop at the White House where Agnew dropped off his resignation letter.

Next they headed to the Baltimore federal courthouse.

It was just after 2 p.m. when Agnew entered that courtroom, already filled with 50 reporters attending a hearing involving the vice president's efforts to force journalists to reveal their sources of leaks about the Justice Department probe. Reporters gasped when they realized the significance of Agnew's appearance.

Agnew's resignation was announced by his attorney, and the former vice president expeditiously pleaded no contest to failing to report $29,500 in federal taxes in 1967. In exchange, federal prosecutors declined to bring far more serious charges of bribery, extortion and conspiracy. (The Justice Department alleged in court papers that Agnew accepted at least $87,500 in kickbacks in exchange for issuing no-bid contracts. A Maryland judge later determined that Agnew had accepted $147,000 in bribes over a two-year span).

Attorney General Elliott Richardson argued that leniency was justified due to the "historic magnitude" of Agnew's resignation and felony conviction. The judge ultimately agreed with the attorney general, sentencing Agnew to three years of probation and ordering him to pay a $10,000 fine.

The hearing was surreal for Parr, who had chased his share of counterfeiters and fraud artists. He recalled feeling shock and disappointment in a man he had so admired.

Forty minutes later, Parr and other agents pushed their way through crowds of onlookers and reporters on their way to the motorcade. Before he could get settled in the front passenger seat, Parr said he heard his radio erupt with the voice of an irate superior.

The official demanded to know why the agency had not been informed Agnew was going to resign. Upon learning from news reports of Agnew's departure, the agency had to scramble to find agents to protect Democratic House Speaker Carl Albert.

"Something could have happened!" the supervisor yelled.

In retrospect, Parr said, he had made a mistake in keeping the secret, writing that "we had allowed ourselves to be drawn in, to the possible detriment of a protectee (Albert), the country, and our careers."

As they drove from the courthouse, the agent heard a murmur from the back seat. Listening carefully, he realized Agnew was reciting a famous Shakespearean soliloquy: "All the world's a stage, and all the men and women merely players; they have their exits and their entrances."