Biological weapons expert Tucker, 56, was known for fluency in politics

Jonathan B. Tucker, 56, one of the country’s foremost experts on biological and chemical weapons and an influential nonproliferation advocate, was found dead July 31 at his home in the District.

A spokeswoman in the District’s Office of the Chief Medical Examiner said determination of the cause of death was pending further investigation.

(Jonathan Winer) - Jonathan B. Tucker, 56, an expert on biological and chemical weapons and an influential nonproliferation advocate, was known as much for his scholarship as for being a policy wonk.

Last year, Dr. Tucker stepped down after nearly 15 years as a research fellow in Washington at what is now the Monterey Institute’s James Martin Center for Nonproliferation Studies. At his death, he was awaiting a security clearance for a new job at the Department of Homeland Security.

A former editor at the journal Scientific American, he wrote authoritative histories on chemical warfare and the eradication of smallpox. In the early 1990s, he worked on arms control and nonproliferation matters at the State Department and the congressional Office of Technology Assessment.

By many accounts, Dr. Tucker possessed a scientist’s probing mind and a policy wonk’s fluency on national security issues. These traits earned him a trusted reputation on Capitol Hill and made him a key source to journalists seeking a credible opinion on biological and chemical weapons.

“Jonathan was a rare breed in that he knew the science of the issue, which was really complicated, and also knew the policy side,” said Paul Carroll, program director at the Ploughshares Fund, a nonproliferation group. “He was one of really a handful of people that could talk to both of these audiences, to both chemists and diplomats.”

In 1995, Dr. Tucker served as a United Nations weapons inspector in Iraq and helped comb laboratories there for lethal germs, noxious gases and other toxic substances. He used his firsthand knowledge of Iraqi leader Saddam Hussein’s chemical weapons program to advise the U.S. government before the invasion of Iraq in early 2003.

Dr. Tucker provided expert testimony to Congress on how he thought Hussein could potentially use his alleged arsenal against the American assault. He said U.N. representatives routinely discovered and destroyed hidden caches of Iraqi biological and chemical weapons after the 1991 Persian Gulf War.

Based on his research, Dr. Tucker told The Washington Post in 2003 that Hussein “may very well use whatever he has” in a “last-ditch defense situation.”

Dr. Tucker added that the artillery systems Hussein used in the Iran-Iraq war of the 1980s had since become obsolete and would not effectively distribute germ weapons.

Hussein “could contaminate areas,” Dr. Tucker said, but any possible usage of the weapons would “only slow the oncoming forces down” because U.S. troops had protective suits.

Ultimately, the precautions were unnecessary. Saddam had dismantled his weapons program years earlier.

Jonathan Brin Tucker was born in Boston on Aug. 2, 1954. He was a 1972 graduate of the private Phillips Academy in Andover, Mass.

He graduated from Yale University three years later with a degree in biology. He received a master’s degree from the University of Pennsylvania before earning a doctorate in nonproliferation studies from the Massachusetts Institute of Technology.

His marriage to Karen Fifer ended in divorce. Survivors include his mother, Deborah Tucker of Cambridge, Mass.; and a sister.

Dr. Tucker’s experience as a weapons inspector helped him to be named in 1995 to the Presidential Advisory Committee on Gulf War Veterans’ Illnesses.

The group was organized to investigate claims that troops who fought in the Persian Gulf War suffered from ailments possibly linked to chemical weapons.

Although he received high performance reviews, Dr. Tucker was dismissed from the team before the report was completed. In interviews afterward, Dr. Tucker said he was removed because he refused to limit his research to data provided solely by the government.

Dr. Tucker continued to investigate independently, conducting interviews with combat veterans and scouring declassified intelligence documents.

In testimony before a House government oversight subcommittee in 1997, Dr. Tucker said he found evidence that suggested Iraq deployed chemical weapons against coalition forces. His report contradicted the findings of the Defense Department and the CIA, which contended that no such armaments were used.

In 2008, the Research Advisory Committee on Gulf War Veterans’ Illnesses found that many of the symptoms veterans exhibited after the Gulf War may have been linked to chemical weapons. The panel concluded that Congress should allocate at least $60 million in funds to research Gulf War veterans’ health issues.

“He was right,” said Jonathan Winer, a former deputy assistant secretary of state for international law enforcement. “Public policy changed.”

Dr. Tucker’s books included “Scourge: The Once and Future Threat of Smallpox” (2001), which traced the virus over 6,000 years, and “War of Nerves: Chemical Warfare from World War I to Al-Qaeda” (2006).

In a New York Times review, author and germ warfare expert Ed Regis called “Scourge” a “concise, suspenseful and scientifically accurate narrative.”

Dr. Tucker’s last book is scheduled for publication early next year. A collaborative effort by 16 international experts, the book focuses on emerging technology and its benefits — and potentially dangerous uses — in the fields of chemistry and biology.