WASHINGTON (AP) — Alexander Butterfield, the White House aide who inadvertently hastened Richard Nixon’s resignation over the Watergate scandal when he revealed that the president had bugged the Oval Office and Cabinet Room and routinely recorded his conversations, has died. He was 99.

His death was confirmed to The Associated Press by his wife, Kim, and John Dean, who served as White House counsel to Nixon during the Watergate scandal and went on to, along with Butterfield, help expose the wrongdoing.

“He had the heavy responsibility of revealing something he was sworn to secrecy on, which is the installation of the Nixon taping system,” Dean said. “He stood up and told the truth.”

As a deputy assistant to the president, Butterfield oversaw the taping system connected to voice-activated listening devices that had been secretly placed in four locations, including Nixon’s office in the Executive Office Building and the presidential retreat at Camp David.

Butterfield later said that, besides himself and the president, he believed that only White House chief of staff H.R. Haldeman, a Haldeman assistant and a handful of Secret Service agents knew about the taping system.

“Everything was taped … as long as the president was in attendance,” Butterfield told Watergate investigators when testifying under oath during a preliminary interview.

The tapes would expose Nixon’s role in the cover-up that followed the burglary in 1972 at the Democratic Party headquarters at the Watergate building. To avoid impeachment by the House, Nixon resigned on Aug. 9, 1974, less than a month after the Supreme Court had ordered him to surrender the relevant tapes to the Watergate special prosecutor.

Butterfield believed he’d had a hand in the president’s fate. “I didn’t like to be the cause of that, but I felt that I was, in a lot of ways,” he said in a 2008 oral history for the Nixon Presidential Library and Museum.