There is rain on the lens and the pictures are jerky, but the action unfolds clearly, one methodical frame per second: Roderick D. Jordan, wearing a hooded white sweater, emerges from the check-cashing store, ducks behind a car and points his gun at Fairfax County police officer Lance T. Guckenberger.

Guckenberger crouches behind his car, aiming his gun as a terrified store clerk crawls beneath the police cruiser for cover. It is a cloudy winter morning; the parking lot along Columbia Pike is wet. The frames click. Jordan fires. Guckenberger, in dark jacket and baseball cap, fires. Jordan falls, wounded in the buttocks, dropping his .40-caliber pistol on the damp macadam.

On Monday afternoon, a jury watched as last winter's soundless gun battle was replayed on a movie screen in a Fairfax County courtroom. The prosecutor called it "the cherry on top" of his case. It was also an example of what some experts say has become one of the richest sources of crime-scene evidence: surveillance camera footage.

"There's more visual evidence at crime scenes today than any other evidence," said Grant Fredericks, a former Vancouver police officer and a forensic video analyst with the nonprofit Law Enforcement and Emergency Services Video Association. "We used to count on fingerprints. Now it's security systems."

One of the first things detectives now do at a crime scene is conduct a sweep for surveillance video that might have captured the incident or the perpetrator, public and private law enforcement officials say. A video security firm in California estimates that there are now 26 million surveillance cameras in the United States generating more than four billion hours of video every week.

"In the absence of any human witness, the video might be your only witness," said Thomas C. Christenberry, a former FBI agent and surveillance video expert at the University of Indianapolis.

Terrorism, murder, kidnapping, robbery, burglary, theft, fraud -- all have been captured on camera. The leaders of the Sept. 11 attacks were caught on film, as were the recent London bombers and the first local killing in the 2002 sniper shootings. There are cameras in banks, schools, parking lots, gas stations, stores, police cars, lobbies and train stations and on highways, rooftops and ATMs.

Security cameras are now such an investigative staple that they have led to the new discipline of forensic video analysis, the art of examining and processing surveillance film. Hundreds of law enforcement agencies across the country now have video analysts, experts say. This past week, in Coeur d'Alene, Idaho, the law enforcement video association hosted a conference it said attracted people from the United States, Europe, Australia and New Zealand.

There are cameras that record, cameras that can zoom in and cameras that can scan. Some can peer in windows. There's a system that can detect a gunshot and quickly aim a camera at the source of the sound. Another can notice things out of the ordinary, such as a package left on a street corner, and send out an alert.

Footage can now be examined for facial features, tattoos, personal mannerisms, jewelry and clothing as well as the license plate, make, model, weight and headlight pattern of a passing car, experts say. Image blurring can often be eliminated, and there is a process called frame averaging in which multiple frames can be blended to achieve one clear picture.

Footage can be used to identify and convict suspects, experts say, and it has a special ability to induce perpetrators to confess. "People, when they're caught on video, are more likely to plead guilty," said Detective Joe Giuffrida, a forensic video examiner with the Maryland-National Capital Park Police. He said suspects recognize themselves on camera more readily than someone else might: "That's definitely me," he said they will realize. "That's the way I walk. That's my posture."

Some investigations, like Washington's recent two-year serial arson probe, have produced thousands of surveillance tapes with countless hours of footage. The video surveillance industry calls this "data overload," and processing it can be mind-bending -- "the fun part," as one federal agent joked.

Legally, there are virtually no limits on camera surveillance in public places, said U.S. District Judge Andre Davis, who was on a law panel at the Idaho conference.

"In the area of public places, movement through public places, there are, constitutionally and statutorally speaking, very, very limited constraints," said Davis, of the U.S. District Court for Maryland. "Some might say there are really no constraints at all.

"That's the law," he said. "On the other hand, there is, shall we say, creepiness about the idea" of constant public exposure to surveillance. "Do we really want to live in a society where every moment of a person's public waking life can be observed and recorded? We're going to have to work all this out."

And the camera isn't perfect. Investigators often find surveillance equipment broken or poorly maintained. "The perception is, 'Oh, great. I've got a tape. I've got pictures,' " said Robert M. Luckett, Alexandria's chief deputy fire marshal and a lead investigator on the serial arson case. "But then you have to spend the time to research what you have in your hand to make sure it's truly applicable."

Sometimes the camera strikes out. "When you don't know what you're looking for, it's difficult," said Dorothy Stout, a Northern Virginia video analyst and consultant. "Not impossible, just difficult." Despite the vast surveillance in the arson case, which included cameras planted by investigators, the culprit, Thomas A. Sweatt, was never filmed, Luckett said: "We never actually saw him on tape."

In the shooting involving the Fairfax County police officer at Baileys Crossroads last January, Jordan, 35, of the District, had asked the clerk in the American Cash Express, also known as ACE, if there were any cameras inside. There weren't, officials said. But there were outside.

While Jordan was busy looking around for a camera inside, clerk Ligia M. Hernandez pressed a silent alarm that summoned police.

When Guckenberger, a former Marine Corps sniper, arrived, Hernandez bolted for safety and Jordan emerged with his pistol. The gunfight that ensued was captured by a surveillance camera on the roof of a Defense Department Missile Defense Agency office across the street.

Security officials there heard the gunshots and with a joystick in a control room focused the camera on the action.

Jurors craned their heads to watch Monday as Deputy Fairfax Commonwealth's Attorney Raymond F. Morrogh showed the 35 stop-action frames in a courtroom with the lights dimmed. "We tried everything to make it clear," he told the jury.

Jordan bobbed behind a parked car, firing eight shots at Guckenberger, according to testimony. Guckenberger fired back six times, yelling at Jordan to drop his gun. Jordan refused, and as he broke from the car and tried to hurry away, Guckenberger felled him with a final shot.

On Wednesday evening, after Morrogh had confronted Jordan on the witness stand with the pictures, the jury found the defendant guilty of attempted capital murder.

"A picture speaks a thousand words," Morrogh later said, "and a video speaks 10,000."

Roderick D. Jordan, wearing a hooded white sweater, emerges from a Baileys Crossroads check-cashing store and aims his gun at Fairfax police officer Lance T. Guckenberger, frames from a video camera show.Another video frame, shown to jurors at Jordan's trial this week, depicts Guckenberger crouching behind a car as a store clerk takes cover. The action was caught on a surveillance camera at an agency across the street.Another frame shows Jordan falling after being shot by Guckenberger and Jordan dropping his .40-caliber pistol. The prosecutor called the camera footage "the cherry on top" of his attempted murder case.