He drove a sleek, $39,000 gray Mercedes, lived in a comfortable ranch house in Great Falls, Va., with his wife and three children, and called himself "Norm Hamilton."

He told his neighbors he was in stocks and real estate.

But the tall, athletically built man with the black mustache had another identity: Bernard Charles Welch, Jr., 40-year-old escaped convict and alleged master thief who D.C. police say shot Dr. Michael Halberstam to death Friday night during a burglary attempt.

Welch supposedly stole only the finest silver, antiques, rare coins and jewelry, and managed to elude the law in at least seven states for the last six years.

Ironically, it took a dying man's gesture of rage to snare one of the most notorious burglary suspects on the East Coast.

"It's really strange," said Arlington police detective Cecil Arnold. "We knew a lot about him, but very little. He [Welch] was almost like a ghost."

A sophisticated, 6-foot-tall figure who police suspected was involved in scores of burglaries around the Washington area for the last five years, Welch's metamorphosis from plumber to antique dealer to suspected master silver thief was pieced together yesterday by law enforcement authorities.

Born in Rochester, N.Y., Welch was a plumber by trade whose first brush with the law involved charges of bad check writing, Arnold said yesterday.

Welch came to Berkeley Springs, W. Va., a small town in the mountains west of Washington, in the late 1960s and opened an antique shop. Arnold recalled the local sheriff thought it strange that Welch was observed bringing antiques and valuables into his shop only at night.

When the sheriff's curiosity led him to check on Welch's background, he discovered a number of outstanding arrest warrants for the antique dealer in three upstate New York counties. Welch was arrested in 1971 and charged with two counts of grand larceny, and one of burglary. He was sentenced to seven to ten years in jail.

On June 14, Welch entered the Clinton Correctional Facility in Dannemora, N.Y., where he was incarcerated for three years. In 1974, he was transferred to the Adirondak Correctional Treatment and Evaluation Center, a medium security facility, where he escaped with a fellow inmate on Sept. 2, 1974.

For the next two years, law enforcement sources said yesterday, Welch and his fellow escapee were suspected of being involved in silver burglaries in New Jersey, Minnesota, Wisconsin and the Washington area.

Arnold said Welch's partner in the escape was a full-blooded Indian. According to FBI records, the man was apprehended in June, 1976, in Charleston, W.Va.

An FBI flyer dated September 30, 1976, described Welch as a fugitive who was involved "in the theft and sale of considerable silverware, coins and antiques. In this regard, Welch reportedly has contacted auctioneers, antique dealers and numismatic exchanges in an effort to sell some of the stolen property."

The flyer also cautioned that Welch was considered "armed and dangerous."

At the time, police believed Welch had already moved to Northern Virginia, where he reportedly continued his particular line of crime.

"He was enthralled with the Georgetown scene," said Arnold. "He liked the historic area."

Two years ago, police and FBI began receiving tips that Welch was often seen at gay bars in Washington.

"He was described as having feminine tendencies," one law enforcement source said yesterday."He was also characterized as being 'a mother's boy.'"

Welch liked to work alone, police said yesterday, and was knowledgeable enough to choose the real silver over silverplate, the expensive baubles over costume jewelry, the genuine antiques over the reproductions.

He also used several aliases, according to the FBI flyer -- among them, "Larry Lee Boone," "John William Landis," "Bernard Miles," and "Myron Henry Snow, Jr." -- while managing to elude local authorities and the FBI, which had compiled what one officer called a "voluminous" file on his suspected involvement in this region's many silver burglaries.

"We've been looking for him for the past five years," said detective Arnold. "But he was so hard to pin down. He was pretty much of a loner."

Last year Welch reportedly purchased a tan brick rambler at 411 Chesapeake Drive in Great Falls, a secluded suburban bedroom community where homes and estates are valued in the $300,000 range. Welch, who told neighbors he was from Duluth, Minn., had started building a large addition onto the house, and an enclosed swimming pool.

He and a woman neighbors knew as his wife, Linda Susan Hamilton, also purchased a 1980 4-door Mercedes SEL 450, which retails for $39,000. Neighbors said yesterday the couple already owned another Mercedes and a station wagon.

Neighbors in the fashionable community were shocked yesterday to learn that "Norm Hamilton," a man they assumed was a wealthy professional, a quiet man who liked to work at home and was the father of a newborn baby, had been arrested for the murder of Dr. Halberstam.

Ironically, Welch's next-door neighbor's house recently had been burglarized. Among the missing items were silver and jewelry. Neighbors said yesterday that police had visited the community Friday afternoon, questioning residents about the burglary.

Among those interviewed was Linda Susan Hamilton.