The District's Office of the Chief Medical Examiner said the cause of death was so far unknown, The Washington Post reported Thursday.
Tucker's body was found July 31. He was 56.
At the time of his death, Tucker was awaiting security clearance so he could take a position in the U.S. Department of Homeland Security.
He left a job of nearly 15 years as a research fellow in the District at the Monterey Institute's James Martin Center for Nonproliferation Studies. He was also a former editor at the magazine Scientific American.
Tucker was often turned to as a source for journalists writing about 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 non-proliferation group. "He was one of really a handful of people that could talk to both of these audiences, to both chemists and diplomats."
Tucker served as a United Nations weapons inspector in Iraq in 1995 and used his knowledge of Saddam Hussein's chemical weapons program to advise the U.S. government before its invasion of Iraq in early 2003.
Jonathan Brin Tucker was born in Boston Aug. 2, 1954. He graduated from the private Phillips Academy in Andover, Mass, in 1972.
Tucker graduated from Yale in 1975 with a biology degree and he earned a master's degree from the University of Pennsylvania before earning a doctorate in non-proliferation studies from the Massachusetts Institute of Technology.