Brian Kelley, 68, a CIA counterintelligence officer who was falsely accused of being a Russian mole in an espionage case that ended in the arrest of perhaps the nation’s most damaging turncoat, FBI agent Robert Hanssen, died Sept. 19 at his home in Vienna.

He had a heart ailment, said his wife, Patricia McCarthy.

Among Washington intelligence circles, the 1990s are known as the decade of deception, when dozens of foreign spies were caught and sent to prison.

Considered the worst among them was CIA counterintelligence analyst Aldrich Ames, who was arrested in 1994 for betraying U.S. informants and selling secrets to Russia.

The scope of Ames’s misdeeds — at least 10 U.S. sources were executed in Russia because of him — brought widespread paranoia to the corridors of the CIA, State Department and FBI. Mr. Kelley, a counterintelligence officer, helped track down the leaks.

Brian Kelley, a Vienna resident and former CIA senior counterintelligence case officer, poses on the bridge in Foxstone Park where convicted spy Robert Hanssen passed classified documents to Russian operatives. (Shamus Ian Fatzinger)

He’d proven his abilities at the CIA in the late 1980s when he uncovered a secret form of communication the Soviets used to contact their covert officers deployed overseas.

Mr. Kelley’s discovery revealed that State Department diplomat Felix Bloch might have worked for Moscow. Yet the suspicions about Bloch were never confirmed. A probe against him failed to gather evidence that would have been admissable in court. Bloch was never charged with any crimes, but he was dismissed from the State Department and lost his government pension.

That Bloch was apparently tipped off about the investigation led many counterintelligence officers, including Mr. Kelley, to believe there was another well-placed Russian spy in Washington.

“No one could figure out who would have tipped off the Russians,” Mr. Kelley told the CBS News show “60 Minutes” in 2003. “We had it so tightly held at CIA that only about seven people knew, and they eliminated everybody but me.”

Mr. Kelley’s life as the suspected Russian agent code-named “gray deceiver” began in August 1999, when he was confronted by FBI officials and accused of espionage — a capital offense.

During an hours-long interrogation at CIA headquarters, Mr. Kelley learned that he had come under FBI scrutiny because he was a mole hunter, like Ames.

Before he was approached by the FBI, Mr. Kelley was the secret focus of an investigation. FBI agents searched his house, combed through his trash and tapped his phones.

Attempting to lure Mr. Kelley into a trap, the FBI sent an undercover agent to his home in Vienna late one night.

When Mr. Kelley opened the door, he told “60 Minutes,” a man speaking in a thick Russian accent told him: “I come from your friends, and we’re concerned. Meet us tomorrow night at the Vienna Metro. A person will approach you. We have a passport for you, and we’ll get you out of the country.”

A break in the investigation came in November 2000 when FBI officials secured tapes of the American spy talking to his Russian handler. The man on the recordings was not Mr. Kelley, but the mole’s voice seemed familiar to the FBI’s analysts.

It was later determined to be Hanssen, a senior FBI counterintelligence agent who had spied for Russia since 1979.

By coincidence, Mr. Kelley knew Hanssen well. They had worked together on several cases and were neighbors. They lived on the same street, blocks away from Nottoway Park, one of the places where Hanssen left documents for the Russians in exchange for $1.4 million in cash and diamonds.

When Hanssen was arrested Feb. 18, 2001, he asked the FBI agents, “What took you so long?”

Mr. Kelley was suspended from the CIA for 21 months during the FBI investigation against him. After Hanssen was arrested, Mr. Kelley rejoined the CIA. He retired in 2007.

Hanssen was sentenced to life in prison in 2002. He burned countless U.S. sources while spying for Russia, including Gen. Dmitri Polyakov, a senior military intelligence figure who was later executed.

Brian Joseph Kelley was born Jan. 8, 1943, in Waterbury, Conn. He was a 1964 graduate of Saint Michael’s College in Vermont. He served in the Air Force’s office of special investigations before retiring as a lieutenant colonel. He joined the CIA in the early 1980s.

His first marriage, to the former Carole Semprini, ended in divorce.

Survivors include his wife of two years, the former Patricia McCarthy, of Vienna; three children from his first marriage, Barry Kelley of Fairfax County, Brian T. Kelley of Herndon and Erin Aldrich of Great Falls; four stepchildren, Nicholas Riegel of Abingdon, Md., Marissa Riegel of Arlington County and Elisabeth Viilu and Brian Riegl, both of Potomac Falls; two sisters; and 10 grandchildren.

In 2003, the Justice Department released an Inspector General’s report calling the FBI’s investigation of Mr. Kelley a failure.

Until his death, Mr. Kelley was a consultant to the U.S. intelligence community, lecturing mole-hunters about the dangers of focusing on the “wrong man.”