Francine Sanders sometimes arrives for work looking nervously over her shoulder. She and her fellow workers at Mount Vernon Realty never leave anyone alone in their Stafford County office. Not since a year ago today.

On Friday, Nov. 14, 1986, Jacqueline Lard, a 40-year-old real estate agent and mother of two, was working late in the office with another woman. As her colleague prepared to leave around 9 p.m., Lard told her: "I'm gathering my stuff; I'll be right behind you."

The next morning, coworkers found blood in the hallway near the back door of their office. Lard's partially clothed body was found one day later by teen-agers in a wooded area off Rte. 1 in Woodbridge, about 20 miles to the north. She had been strangled and badly beaten, and her body was rolled in a carpet and covered with leaves, according to police.

"I was never afraid of anything before this," Sanders, a former Marine who joined Mount Vernon Realty about two weeks before Lard's slaying, said this week. "Now . . . I'll never come around here by myself. If I come here in the morning and nobody's here, I wait in my car."

One year after Lard's death -- after 2,300 interviews, 200 suspects, the use of hypnosis on two potential witnesses and a $20,000 reward offered by a realty agents group -- no one has been charged in the case, which has involved the Prince William County police, the Stafford County Sheriff's Department, the FBI and the Drug Enforcement Administration.

Jacqueline Lard's husband Ron, a DEA employe, was out of the country at the time of her death. Authorities do not believe her murder had anything to do with his work. Ron Lard declined to be interviewed for this story.

"We have been on a roller-coaster ride since the investigation began," said William T. Healey, a special agent with the DEA.

Officials this week released sketches of a man who may have information about the slaying.

The sketches are based on information provided by two persons who say that on the weekend Lard was killed they saw a man -- whom they described as about 6 feet tall, in his mid-twenties, heavy-set with acne scars -- in the vicinity of the dirt and gravel dead-end road where the body was found.

Although investigators will not describe the man as a suspect, his age, build and height are similar to what was listed in an FBI profile of the killer.

Police do not think the killer knew his victim, and describe the killing as "a crime of opportunity." This has made the case extremely difficult to solve, according to sources close to the investigation.

Healey said the killer overcame the initial panic that usually follows a homicide and began a "thinking phase," which included taking Lard's body to another county and leaving it in an out-of-the-way spot. He then drove her 1986 Nissan 25 miles to the Bren Mar Apartments in Alexandria, where it was found Dec. 18.

In addition, police say the killer attempted to remove any incriminating evidence such as fingerprints and hair.

Investigators have used microscopes, computers and laser technology to look for and examine hair, fingerprints and fibers in the case. They even know what kind of sneakers the killer wore that night.

"We have the evidence to make this case," said Prince William investigator Robert Zinn. "In fact, we have been able to exonerate some promising suspects."

"Making" the case hinges on finding a key witness, according to investigators, who have set up a 24-hour hot line and mailed 50,000 fliers.

"Somebody out there knows something," Zinn said. "Somebody out there holds the key."

Anyone who knows the killer and what he has done is in danger, authorities said, especially near the anniversary of the crime, when the killer may be feeling anxious. Investigators also said that the killer has likely been involved in sexual assaults since Lard's death, and could kill again.

"Once a person crosses that threshold of violence, I ask you, is it easier to do again? We are not trying to cause a panic, but people should be careful," said Zinn.At the Stafford County office where Lard once worked, that message needs no repeating. "We have really banded together," said Jim McLain, 36. "We try to look out for each other. We make sure no one is ever in the building alone. We've got a new security system as well."

Sanders, 37, said she thinks about Lard "all the time. I pray for her. And I pray that whoever did it gets caught."