The tipster showed up at the Fairfax County police station Saturday with some unusual and chilling information: A 1986 red Toyota MR-2 was on its way to the Lorton area at that very moment with a homicide victim in the trunk.

The person seemed credible, and officers at the West Springfield District station acted on the tip immediately. Police began searching the Lorton area, and within about 15 minutes spotted a 1986 red Toyota MR-2--one with a body in the trunk.

Fairfax police, who stopped the car in the 9400 block of Gunston Cove Road, said yesterday that they were able to determine that the man in the trunk had been killed in Spotsylvania County, and law enforcement officials there have taken over the case.

Maj. Howard Smith, of the Spotsylvania County Sheriff's Office, identified the victim as Lawrence Matthew Kersey IV, 21, of Caroline County. Kersey was an acquaintance of both occupants of the car, who have been charged with first-degree murder and robbery, he said.

The suspects, Teresa M. Haynes, 32, and William T. Hayes Jr., 27, both live in Caroline County and were dating, Smith said. He declined to say whether investigators have determined a motive in the slaying.

Smith said Fairfax police called the Spotsylvania sheriff's office Saturday night to alert them to their first homicide of the year after talking to the car's occupants. Detectives were sent immediately to Fairfax, where they also interviewed the pair.

"Based on those interviews, they were able to locate the murder scene," Smith said. Detectives believe Kersey was slain on the side of Mallard Road, an isolated rural road, just over the Caroline County line in Spotsylvania, and that he was killed with a blunt object, he said.

An autopsy will be performed today to determine the cause of death, Smith said.

Haynes and Hayes were being held without bond at the Rappahannock Regional Jail, he said.

They are to be arraigned on the felony charges today in Spotsylvania County General District Court.

To protect their tipster, Fairfax police declined to identify the person's gender. But they said that the tipster gave them detailed information and that they took it seriously.

"We don't get tips telling us about a homicide before we have a body," said Lt. Mike Fish, a police spokesman. "When the tipster went in to talk to the officer, he didn't blow [the tipster] off."

The two suspects were headed to Fairfax County, but Smith declined to identify their exact destination. The vehicle was stopped about 5:15 p.m. near a car-towing business, close to Route 1.

Smith said the two were also charged with robbery because money was stolen from the victim. The car was registered in Haynes's name, he said.

Fairfax police will continue to assist Spotsylvania officers in their investigation, Fish said.

Fish praised his colleagues for fast action on the tip given to police.

Because they "acted quickly and promptly, they were able to take the two people into custody without incident," Fish said.