When Prince William County prosecutors were trying to convict Roy Bruce Smith of slaying Manassas policeman John D. Conner III last year, testimony from neighbors that he had fired shots into the air and made wild statements about wanting to shoot a policeman was enough to convince a jury of his guilt.

But in seeking the electric chair for Smith, Commonwealth's Attorney Paul Ebert also needed to prove that Smith had premeditated the killing of a police officer when he shot Conner to death on July 24, 1988.

Premeditated murder is not necessarily punishable by death, but murdering a police officer during the commission of his duties is a capital offense in Virginia.

The extra bit of evidence Ebert needed -- the proof that eventually landed Smith on Virginia's death row -- was secured by a computerized information system operated by the FBI.

Using data compiled and analyzed by the National Crime Information Center, or NCIC, law enforcement officials "were able to introduce evidence that this fellow was a cop hater and had had recent run-ins with police where he threatened them in two different states," Ebert said.

Ebert said the NCIC found that Smith had threatened to kill a police officer in California and had been convicted of assaulting a police officer in Massachusetts -- information not on his criminal record when local authorities initially checked it.

The NCIC system's ability to find valuable information is being chronicled in a film scheduled to be shown to police departments nationwide on Sept. 12 during a satellite training program.

Last week, producers working on the film came to Prince William County to reenact Conner's murder and the subsequent investigation and to interview Ebert on how the NCIC helped him convince a jury that Smith should die.

"We had enough evidence for a conviction, but his defense {against the death penalty} was that he didn't know he was shooting a cop," Ebert said. "If his attorney had been able to convince a jury of that, it wouldn't have been capital murder."

The NCIC is a computerized information network linked to 64,000 law enforcement agencies with data banks containing 20 million crime-related records. When a police officer linked to the system stops a driver on a routine traffic violation, the FBI computer check is run within seconds to determine whether an arrest warrant is outstanding for the driver or whether the car is stolen.

About 1 million transactions are run on the network daily. The cost to taxpayers for a police check is 3 cents, said NCIC chief David Nemecek.

The program has an annual federal budget of $8 million. The states pay a total of $200 million to $300 million each year to be linked to the system and to run information checks, he said.

The NCIC, which includes 60,000 computer terminals nationwide, was established in January 1967 as an alternative to the old teletype communications system used by police agencies to exchange information, officials said.

It is responsible for the recovery of $1.1 billion in stolen vehicles and the location of 136,000 fugitives each year, Nemecek said.

The system is operating on the same technology that was installed 23 years ago, Nemecek said. Congress is considering a $17 million allocation to the Justice Department to revamp the system, said Rep. Don Edwards (D-Calif.), chairman of the House subcommittee that monitors the FBI. The cost to upgrade the system is expected to reach $75.5 million over the next five years, he said.

"This will have no problem passing," Edwards said, adding that a previous request was denied because the Office of Management and Budget and other officials were concerned that some upgrades the FBI had proposed might have violated privacy rights.

NCIC officials said the system's software will be updated and more advanced capabilities will be added, including a system that would allow officers to receive photographs and match fingerprints in the field on a special "magic box," Nemecek said.

That system would require specially equipped cars furnished with approximately $3,000 in mechanisms, including cameras and printers, he said.

FBI officials believe the additional identification capabilities will cut down on faulty arrests that have resulted from NCIC information by providing more foolproof identification methods, Nemecek said.

The film under preparation will highlight the Prince William County case and how the computer system played a part in Smith's sentencing. The purpose is to encourage police to use the more complex features of the system, officials said.

"We are going to talk about not only how NCIC can assist in making inquiries, but on all the investigative support that the system can provide as well," Nemecek said, adding that the network has the capability to do complex analyses of the data in the computers' banks.

Alexandria Deputy Commonwealth's Attorney Randy Sengel said that the NCIC helped his agency track a police killer 10 years ago. Like Smith, the perpetrator was sentenced to death after his prior run-ins with police were disclosed.

Sengel said Virginia laws don't allow prior arrests to be introduced into evidence in most cases, but he emphasized the importance of prior arrests and convictions when judges allow their introduction in death penalty cases.

In Los Angeles County, where prior convictions can be used to impeach the testimony of defendants who testify during their trials and to enhance penalties for convicts, the NCIC is used regularly to disclose defendants' records in other states, said Assistant District Attorney Curt Livesay.

"If a defendant is convicted of a crime in another state that would be a crime in California, we can use that conviction," said Los Angeles County Deputy District Attorney Robert B. Foltz. "Since criminals rarely feel bound by state lines, the NCIC allows us to have information about them from around the country, instead of just being limited to information from this state."

Vail, Colo., police Lt. Jeff Layman said the system is especially helpful to small police agencies in tracking down fugitives because they don't have manpower or resources to chase suspects.

Fugitives from Vail wanted for armed robbery and kidnapping are listed in the NCIC files, Layman said.

"We have mostly bar fights and burglaries -- very little violent crime," Layman said. "But when we do and they leave, the NCIC is the best way for us to try to get them back here."

Computer Network: Facts and Figures

Transactions per day: 1 million.

Law enforcement agencies linked: 64,000.

Crime-related records contained in system: 20 million.

Length of time to check for stolen car: 2 seconds.

Length of time to check suspect for criminal record: 2 seconds.

Number of stolen cars returned because of NCIC information each year: 169,000.

Number of fugitives located through system each year: 136,000.

Cost to federal government for each police check: 3 cents.

Computer terminals in use: 60,000.

Annual budget from federal government: $8 million.

Cost to local governments to use system: $200-300 million combined.

Capabilities most used: check criminal records, stolen goods, outstanding warrants, provide information on missing persons.

Source: FBI National Crime Information Center