Larry McCann believes a serial killer is responsible for the deaths of six people and the disappearance of two others, and even though the slayings apparently have stopped, the state police psychologist thinks the killer is still out there.

Typically, ``somebody of this type doesn't just stop. If the killings stop that means he's either died, gone to jail or moved out of the area,'' said McCann, a behavioral psychologist.

But in this case, McCann believes the killer may have been stymied by the death of an accomplice. A search of the FBI database on violent crimes shows there have been no killings in the past 2 1/2 years anywhere in the United States, Canada or Australia that fit the pattern of the Virginia crimes. Interpol also reports no similar crimes in Europe.

That indicates to McCann that the killer is not operating elsewhere unless it is in the Third World.

McCann said if the killer has died, police probably will never know. ``If that is the case, it was likely a violent death. Violent lives generally end in violent deaths,'' he said.

If the killer is in jail, McCann said the pattern of killing probably will resume when the killer is released.

Two years ago, McCann and the FBI went public with their belief that the killings of three couples and the disappearance of a fourth in the general vicinity of the historic Colonial Parkway were the work of one person.

After an extensive study of the four crime scenes, McCann compiled a psychological profile of the killer. McCann declines to discuss the specifics of the profile.

``There is some behavior that tells us something about this man that we just don't want to release,'' he said.

Two years ago, McCann said there was a second person who had an ``intimate knowledge'' of the crimes. He implied that the second person might be in danger.

McCann said last week that his statements two years ago were intended to warn the second person.

``I was trying to let this person know, `Hey, you're next on his list,''' McCann said. ``It's a pretty good possibility that that second person is dead.''

From his study of the crime scenes, McCann concludes the second person may have been a helper to the killer.

``I don't think one person could have controlled the victims,'' he said. ``I think there needed to be two. These were not easy targets. These were young, healthy, strong individuals. It would have been too much for one person to handle.''

The crimes began in October 1986 with the killings of Cathleen Thomas, 28, of Norfolk and Rebecca Dowski, 21 and a student at the College of William and Mary, on the Colonial Parkway near Williamsburg.

The women were found in the back seat of Thomas' car. They had been strangled and their throats slit. There were no signs of a struggle, nor had the women been raped or robbed.

Thomas' car had been pushed over an embankment along the parkway.

In September 1987, the bodies of David Knobling, 20, and Robin Edwards, 14, both of Newport News, were found at the Ragged Island Game Refuge on the James River. Each had been shot in the back of the head. Again there was no sign of a struggle.

Knobling's pickup truck was found in the refuge parking lot with its keys in the ignition. His wallet was found on the truck's seat.