They have broken into homes, offices, hotel rooms and automobiles. Copied private computer files. Installed hidden cameras. Listened with microphones in one couple's bedroom for more than a year. Rummaged through luggage. Eavesdropped on telephone conversations.
It's the FBI, operating with permission from a secretive U.S. court in a high-stakes effort pitting the nation's premier law enforcement agency against the world's spies and terrorists.
Most Americans never see this side of the FBI.
"The average citizen has no idea whether information about them might be caught up in one of these investigations," said David Sobel of the Washington-based Electronic Privacy Information Center, an expert on this type of surveillance.
The Foreign Intelligence Surveillance Act — enacted in 1978 and strengthened after Sept. 11, 2001, by the PATRIOT Act — gives investigators a potent arsenal against "agents of a foreign power." The Bush administration this week won an important court victory affirming its plans to expand these tactics to more cases.
Besides break-ins, agents have pried into safe deposit boxes, watched from afar with video cameras and binoculars and intercepted e-mails. They have planted microphones, computer bugs and other high-tech tracking devices.
"The whole thing is very, very mysterious and quiet," said Plato Cacheris, the Washington lawyer who represented spies Aldrich Ames and Robert Hanssen. "There's not a lot that anyone can tell you."
Surveillance is a deadly serious game among the trench-coat set featuring "black bag" jobs and wiretaps. Their 007-like gadgets — one captures every keystroke typed on a target's computer — and the specialized agents who use them are among the best available.
These tools and the law are "designed to target intelligence officers and people trained by intelligence officers," said Michael Woods, a former senior FBI lawyer who coordinated many investigations.
Nearly all those known to have been targeted did not detect what was happening until FBI agents flashed guns and badges.
The bureau is cautious. Agents never broke into Hanssen's home in the Washington suburbs because they couldn't find time when his wife or children weren't there, according to people familiar with the case.
"They're very good at not getting found out," said Nina Ginsberg, a lawyer in Alexandria, Va., who has represented three people under surveillance. "I'm sure they would sit outside a house for a week before they made sure they could go in."
The FBI watched Therese Marie Squillacote, a Defense Department lawyer, and her husband for 18 months. Over that time, they broke into their home three times and planted a microphone in their bedroom to monitor their conversations, according to court records. She was sentenced in 1999 to nearly 22 years for attempting to spy for East Germany and Russia with her husband.
What little is known about these FBI techniques emerges from court records spread across dozens of cases. But only a fraction of these nearly 1,000 surveillances each year result in any kind of public disclosure, so little is known outside classified circles about how they work.
Convinced that a longtime Defense Department analyst was spying for Cuba, the FBI sneaked into her apartment in northwest Washington last year to search her bedroom and make a secret copy of all the files on her aging laptop.
They went back six weeks later to look around, while other agents secretly watched her elsewhere. And the FBI rifled through her purse and wallet one week after that. Their evidence haul: e-mails and codes describing espionage, a shortwave radio and a prepaid calling card used to send spy messages over pay phones. Ana Belen Montes pleaded guilty and was sentenced last month to 25 years in prison.
One message found on her computer was prescient advice from Cuban agents warning her not to leave anything where spy-hunters might find it: "Do not leave prepared information that is not ciphered in the house. This is the most sensitive and compromising information that you hold."
FBI microphones in another case recorded a murder. Surveillance of suspected terrorists in St. Louis captured one man fatally stabbing his teenage daughter 13 times with a butcher knife while shouting, "Die! Die quickly!"
Stunned FBI agents handed over the recording to Missouri prosecutors, who convicted the man and his wife. He died of an illness in 1997 on death row.
Sometimes the FBI overreaches. An FBI memo that surfaced last month said agents in early 2000 illegally videotaped suspects, intercepted e-mails without court permission and recorded the wrong phone conversations. In one case, the FBI listened on conversations long after its target gave up a cell phone and its number was reassigned to an innocent person.
Hanssen, sentenced to life in prison for spying for Russia, insists a transmitter the FBI tucked inside his 1997 Ford Taurus "chirped" once while he was driving through a parking garage. Although the FBI denies it, Hanssen maintains he knew weeks before his arrest that he was being followed.
And Earl Edwin Pitts, another FBI agent convicted of spying for Russia, discovered a surveillance camera hidden in the ceiling of his office at the FBI's training academy but continued his espionage after agents allayed his suspicions.
Legal experts said this week's court decision will lead to increasing use of the surveillance law.
"We're going to do everything we can to identify those who would hurt us to disrupt them, to delay them, to defeat them," Attorney General John Ashcroft said.