NORFOLK, JULY 23 -- Authorities say someone other than the killer has an "intimate knowledge" of a four-year string of killings and disappearances in southeastern Virginia and asked today for that person's help.

"It's time for that person to come forward. It's in his best interests. He has an intimate knowledge of these crimes," Larry McCann, a state police behavorial pyschologist, said at a news conference here.

Irvin B. Wells, FBI special agent in charge of the Norfolk office, said the killings of six young people and the disappearance of two others may be connected.

"The Center for the Analysis of Violent Crimes at the FBI headquarters in Quantico believes there is a chance that the four incidents are connected. We believe there is someone, somewhere who has information about these crimes or has personally witnessed a threatening occurrence that involved an authority figure," Wells said.

Wells said evidence from the crime scenes seems to show that "control of the victims was probably taken early on in the crime." He said that could have been done by someone posing as a police officer or by pointing a gun in the victim's face.

The crimes began in October 1986 with the slayings 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. They had been strangled and their throats slit.

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. There was no sign of a struggle.

In April 1988, not far from the site of the Thomas and Dowski killings, Richard Call, 20, of Gloucester County, and Cassandra Hailey, 19 and a student at Christopher Newport College, disappeared.

In September 1989 near Interstate 64 in New Kent County, Daniel Lauer, 21, of Amelia County, and Annamaria Phelps, 19, of Virginia Beach, were reported missing. Their bodies were discovered in a nearby wooded area about a month later. They had been stabbed.