Washington By bugging a keyboard or using special software, FBI agents can remotely capture a computer user's every keystroke.
With a black box, they can intercept e-mail from miles away.
In a van parked outside, they secretly can re-create the pictures on a computer screen from its electromagnetic energy.
The legal limits for these new investigative tools will get a test Monday when a federal court in New Jersey examines a mob case in which agents, without a wiretap order, recorded a suspect's computer keystrokes.
Privacy experts are watching the case of Nicodemo S. Scarfo Jr. with great interest because it could bring major changes to investigative tactics in the online age.
"It's the idea of secret government surveillance technology being installed with very little oversight or accountability," David Sobel of the Washington-based Electronic Privacy Information Center said. "It gets about as close to the common perception of Big Brother as anything I could really imagine."
Armed only with a search warrant, the FBI broke into Scarfo's business and put either a program on his computer or an electronic bug in his keyboard officials will not say which and recorded everything typed by the son of the jailed former boss of the Philadelphia mob.
The FBI says it needed a password in order to decrypt coded files that allegedly contained records of illegal gambling and loan-sharking operations.
Scarfo used the software PGP Pretty Good Privacy to encode his records. PGP is a strong, free encryption program that can be used for e-mail or individual files. The FBI tried to break the encryption without the password, but failed. So agents surreptitiously bugged the computer to capture it from Scarfo himself.
Scarfo's lawyer wants a Newark, N.J., federal court to suppress the evidence and make the FBI say how the bug worked. The lawyer says that because the FBI recorded everything Scarfo typed, they got private e-mails that were not part of the investigation.
U.S. Atty. Robert J. Cleary has told the court that the surveillance device is a "highly sensitive law enforcement search and seizure technique" and should not be made public.
Mark Rasch, former head of the Justice Department's computer crimes section, said that if the device transmitted the captured keystrokes back to the police via e-mail, or emitted them through radio signals, then it might be considered a wiretap.
"You really need to understand at what point it captured things, and how it got it back to the government, in order to figure out what the Fourth Amendment concerns are," Rasch said.
Authorities have to meet a much higher standard for a full wiretap, which includes filtering out nonrelevant communications and having stronger proof that a crime is taking place.
The government argues it only needed a search warrant for Scarfo's computer because the captured keystrokes were not immediately being transmitted on the phone line or on the Internet, and should not be considered the products of a wiretap.
There are many tools the FBI can use for secretly capturing computer information.
Earlier this year, the FBI used a keystroke bug to nab two Russians suspected of hacking into U.S. Internet companies. The Russians have not yet gone to trial.
In addition to the keystroke logger, technicians can sneak in a program that will take intermittent snapshots of the monitor, or install a hidden camera pointed at the computer.
There is even a system called TEMPEST that detects electromagnetic emanations from a computer monitor. Agents in a van parked outside can then reconstruct the desktop.
The FBI also has received widespread attention for a device formerly known as Carnivore and now called DCS 1000 that can follow suspects' Web browsing, e-mail and instant messages.
"If they can find a way to read your mail or peek in your bedroom and find a way for a judge to authorize them to do it, they will do it," Rasch said.
The Supreme Court recently reined in one high-tech tactic when it ruled police needed a warrant to use a special heat-sensing device to discover that a man was growing marijuana in his home.
However the Scarfo case ends, Sobel said, the high-tech crime landscape is bound to change.
"I think it has significant implications for future law enforcement investigations," he said. "This type of investigation is the wave of the future."