The U.S. District Court jury deliberated 24 hours over five days before returning the verdict.
The jury then resumed deliberations on whether Regan offered Iraq documents concerning nuclear weaponry, military satellites, war plans or other major U.S. weapons systems. After an hour, the panel recessed until Monday without reaching a decision.
If the jury finds that he offered those secrets, he could be subject to the death penalty. Jurors would hear a second round of testimony to consider such a sentence.
Ethel and Julius Rosenberg were the last Americans put to death for spying. They were executed in 1953 for conspiring to steal U.S. atomic secrets for the Soviet Union.
Regan, a 40-year-old married father of four from Bowie, Md., was arrested Aug. 23, 2001, at Dulles International Airport outside Washington while boarding a flight for Zurich, Switzerland.
He was carrying information with the coded coordinates of Iraqi and Chinese missile sites, the missiles that were stored there, and the date the information was obtained, prosecutors said. He also had the addresses of the Chinese and Iraqi embassies in Switzerland and Austria in his wallet and tucked into his right shoe.
Regan had worked at the National Reconnaissance Office, which operates the government's spy satellites, first for the Air Force and then as a civilian employee for TRW, a defense contractor.
It was unusual for the case to even reach trial. The government, wary of disclosing classified material in public, normally agrees to plea bargains in espionage cases.
It also was surprising that the government sought the death penalty in a case where prosecutors acknowledged sensitive material never was passed. In cases much more damaging to the government, the CIA's Aldrich Ames and the FBI's Robert Hanssen were sentenced to life in prison.
Special security measures were used in the Regan case, with a machine resembling a high-tech overhead projector displaying secret documents on monitors that the jury could see but the public could not.
Prosecutors said Regan owed nearly $117,000 on his credit cards when he wrote a letter to Iraqi leader Saddam Hussein offering to sell satellite intelligence that could help Iraq hide anti-aircraft missiles. His asking price was $13 million.
The letter was found on a computer taken from Regan's home after his arrest. The computer contained a nearly identical letter to Libyan leader Moammar Gadhafi, prosecutors said.
During the two-week trial, government witnesses portrayed Regan as a man desperate to get out of debt and willing to sell American secrets.
Using his access to a classified Internet network, Regan looked up dozens of top-secret documents, including satellite photos of Iraqi missile sites and confidential documents about Libya's biological warfare program, the prosecution said.
Defense lawyers said Regan might have fantasized about spying, but never copied anything of value and had no real intention of selling secrets. Attorney Nina Ginsberg called his actions "childish," "unprofessional," "nonsense" and "harebrained."
"No serious foreign power would ever want to deal with this person," Ginsberg said in her closing argument.
Assistant U.S. Attorney Patricia Haynes, in her final presentation to the jury, argued Regan was not playing spy.
"Brian Regan is not a fantasizer," she said. "Brian Regan is a traitor."
Government witnesses said if Regan passed the information he was accused of possessing, American security would be compromised and U.S. and British pilots who patrol the no-fly zones in Iraq could be endangered.
The defense argued that Regan wasn't carrying anything of value when arrested.
"The information was not terribly significant," said Maynard Anderson, former acting deputy undersecretary of defense for security policy. "It did not provide anyone any information that was not publicly known."
Defense lawyers also argued that Regan was doing research to keep him current on topics he once specialized in. His resume, for example, said he evaluated "all sources of intelligence on Iraqi operations."
They contended it was not unusual for employees with access to classified material to look up information about countries in the news, such as Iraq.
Jury Deliberates Charges He Tried To Sell Data To Iraq, Libya, China