D.C. police Detective Mike Miller felt anxious as he and other officers huddled around a computer and waited for data to spill from a "black box" recovered from a car involved in a wreck that killed a 49-year-old financial adviser.

Just a decade ago, detectives investigating traffic accidents would analyze skid marks with tape measures, rulers and special wheels. They painstakingly plotted the data on graph paper and sometimes had to ask graphic artists to render a scene for a court exhibit. Now they use lasers and computer analyses that measure and map the split-second anatomy of a crash.

And, like their counterparts in aviation circles, they are turning to black boxes -- event data recorders that carmakers have tucked into millions of vehicles. The recorders can be a treasure for police: They can reveal the speed, braking and throttle of vehicles in the seconds before impact. The black boxes are no secret within the auto industry, but many motorists remain unaware of them.

As the computer screen flashed to life, Miller leaned forward. He wondered whether his earlier calculations about the cars' speeds -- based on the lasers and computer analysis of the scene -- would prove to be correct. He knew that the black box's data could be the key in moving forward with a homicide case.

The moment highlighted the evolving nature of traffic investigations. With the help of lasers, Miller and other investigators can calculate distances to within a 10th of an inch. Computer databases provide reams of information about how cars react when struck. Software allows investigators to create maps.

The emerging technology "has made the job more technical and more professional," said Miller, who has been investigating car crashes for 13 of his 15 years on the force. "It's a new realm."

Miller and Detective Joseph Diliberto said the advances have helped them get to the bottom of a greater percentage of the city's fatal accidents. Last year, the city had 45 traffic deaths.

"It can help sway an investigation one way or another," said Diliberto, who has helped reconstruct fatal crashes since 1991. "It can help define whether there is criminal culpability."

Most of the area's suburban departments are using the same new tools. Arlington County and Virginia State Police investigators used a laser device to help map the scene of a school bus crash that killed two children and injured 15 others in April.

In Fairfax County, where police investigated 61 fatal crashes last year, officers said the technology helps them keep pace with cars that are more apt to have anti-lock brakes, air bags and traction-control devices. "As the level of sophistication that exists in the automobile increases, investigators have to keep up with the technology," said Sgt. Pat Wimberly, who supervises Fairfax's accident investigators.

The Washington Post trailed Miller as he investigated several traffic accidents, including his follow-up work on the one that killed the financial adviser Nov. 30. Despite the technology, the cases can be time-consuming: It was not until last month that a man was indicted on a second-degree murder charge in that collision.

Miller was asleep at home early Nov. 30 when he was called to report to Park Place and Irving Street NW, the site of the accident. When he got there, he learned that a Buick LeSabre had zipped through a red light and crashed broadside into a Mercury Grand Marquis about 12:55 a.m., according to police officers and witnesses.

The Mercury's driver, John C. Johnson Jr., was on his way to pick up his sister from work when the crash occurred, sending his car skidding 150 feet down the road and over a patch of grass. Johnson, who was described by relatives as a good-hearted man who always put family first, was killed almost instantly.

His Mercury was crumpled -- the driver's side crushed, computer components and wires dangling from the dashboard, the remnants of an air bag and metal jutting in all directions. The Buick's front end was smashed.

In an interview later, Miller described what he did at the scene. After a quick scan of the intersection, he took out a laser device known as "Total Station," which works much like a surveying tool. For several hours, Miller shot the laser from a specific point to a prism being held by a police technician, allowing him to quickly tabulate distances and carefully map the scene.

He marked skid marks, debris fields, furrows in the grass, trees, streetlights and even bushes. Without the laser, Miller and the technician would have spent four hours evaluating the scene with tape measures and calibrated wheels. Once the information was uploaded into a computer, it would generate a map of the scene, showing the precise location of each object.

Based on the preliminary examination, police arrested the Buick's driver, Guy B. Agnant, 22, of Lanham, and charged him with second-degree murder and illegal possession of a handgun, which authorities said was found under the front seat. The case later went to a grand jury, which returned an indictment on murder and gun charges.

Agnant, who was seriously injured in the wreck, pleaded not guilty to the charges and is awaiting trial in D.C. Superior Court. He is under house arrest as he recovers from his injuries, said Robert C. Bonsib, Agnant's defense attorney.

Bonsib said he and his client would not comment because the case is pending.

Despite all the work done at the crash scene, Miller had plenty of additional investigation to complete before the prosecution moved forward. In early February, as he handled a half-dozen other cases, he jumped back into the probe. Accompanied by a Post reporter, he visited the city's impound lot, took laser measurements and closely inspected the two mangled cars.

Using the laser device, Miller and Officer Anthony Maturo, a crime scene technician from the Secret Service experienced in fatal crashes and assigned to the case by the U.S. attorney's office, measured the dents in the cars. The measurements later would help Miller more precisely plot the cars on a map showing their locations before, during and after the collision.

That week, Miller and Maturo also had a tow truck put the cars together, as if at impact. They then took some overhead photographs to show how the cars fit together.

The detective then removed the black box -- actually silver, in this case -- from the Buick's center console. The device helps deploy the car's air bags and monitors various systems. During a crash, it collects the last five seconds of data -- ranging from the car's speed to its throttle position -- and locks the information into its memory.

Most General Motors and Ford vehicles carry such recorders. About 33 million cars on U.S. roads, or 15 percent, have them, according to the automotive industry. But this was the first time that Miller had used one to investigate a fatal wreck. It is also the first time that D.C. prosecutors intend to use the device's data in a criminal case, authorities said.

On a February morning, a week after visiting the impound lot, Miller and Maturo drove to Fairfax, which has the software and equipment required to read event data recorders. Miller said D.C. police are trying to buy such software but have been unable to come up with the funds.

The Fairfax officers plugged the device into a laptop computer, which quickly hummed to life.

A graph popped onto the screen. It showed the Buick going 81 mph about five seconds before impact. The instant before the crash, the Buick was traveling 91 mph.

Miller began to ponder the meaning behind the new data, which showed the Buick accelerating, not slowing, before impact. Miller and the other officers quickly theorized that the driver was hurrying to make it through the intersection before the light turned red. It was a detailed piece of evidence that Miller said was not available in the past.

Miller took a breath and smiled. His previous work had been amazingly accurate.

"It's one table leg of the entire investigation," Miller said of the black box.

Then he began talking more like an engineer and less like a police officer: "When you put it all together, you have a very stable platform that shows how the crash occurred and why it occurred."

Reconstructing a crime scene, a laser device helps D.C. Detective Mike Miller tabulate distances and carefully map objects.D.C. Detective Mike Miller, center, consults with Secret Service officers while gathering crime scene evidence with electronic devices.