Nearly seven years after three young women were found murdered in a real estate office-trailer near Dale City, the case is unsolved.

Prince William County police and prosecutors long have said they have a suspect in the case, but not enough evidence against him to bring an indictment. The investigation is no longer active, they say.

The murders were three of the most ghastly and inexplicable crimes ever recorded in Northern Virginia and they touched off a massive police investigation. For a time, virtually every investigator in the Prince William County police department was assigned to the case.

The investigation "changed the lives of a lot of people who worked on it," said Lt. C.T. Deane, a Prince William police officer formerly assigned to the investigation.

The three women were found lying side by side on the floor of the trailer in the evening of June 24, 1978. Each had been shot once in the back of the head with a handgun. Their purses had been rifled, but their was no sign of struggle or sexual assault.

One of the victims, Karen Rose Scarbrough, was a 17-year-old Fredericksburg, Va., native who had just graduated from high school and was on her first day of work as a receptionist in the Ryland Homes real estate trailer.

The other two -- Sharon Lake, 25, and Deborah Warner Frank, 23 -- were friends whose husbands worked together at the Pentagon. Lake, from Dale City, was a first-grade teacher, and Frank, from Alexandria, worked for a McLean consulting firm.

Police theorized that Lake and Frank walked into the trailer to pick up literature on houses in the area and may have stumbled on a robbery or intended rape.

But officers say they do not know for sure how the incident turned into a triple slaying. "Maybe he panicked; maybe there were drugs in him; we just don't know," said an investigator who was assigned to the case.

The man who police and prosecutors generally agree is the top suspect in the case was seen in the area of the trailer the afternoon of the killings. They say he contradicted himself in interviews with law enforcement officials but there was never enough evidence to charge him.