On March 1, 1976, William Bradford Bishop Jr., an ambitious State Department official, reported for work complaining of a cold. After a longer-than-usual lunch, during which he withdrew $400 from a savings account, he told his secretary he was leaving early.

On his way home Bishop stopped at the Montgomery Mall shopping center, where he bought a gasoline can and a ball peen hammer. He filled the can and the tank of the family's maroon Chevrolet Malibu station wagon with gasoline at the Texaco station at the edge of the mall parking lot, and arrived home about dusk.

Later that evening, five members of Bishop's family -- his mother, Lobelia, aged 68; his wife, Annette, 37, and their three sons, Brad, 14, Brenton, 10, and Geoffrey, 5, -- were beaten to death in their comfortable contemporary home in the Carderock Springs section of Bethesda.

Bishop, who was charged with the slaying three weeks later, has been missing ever since.

In the five years that have elapsed, the vanished diplomat has been the inspiration for a song and a novel, and the subject of thousands of leads. The most recent tips of consequence placed Bishop in Stockholm, Sweden and Sorrento, Italy, and Montgomery County police Cpl. Clem M. Orbin still checks out two or three "sightings" of Bishop each month.

Orbin says he is convinced that Bishop is still alive. But he admits, and FBI agents who have followed the case agree, that they have no leads -- never have had a good lead -- on the killings that rocked the Washington diplomatic community and ended what had appeared to have been an idyllic, all-American family.

Bishop, who is now 44 if he is still alive, and his wife were among the most popular couples in the upwardly mobile neighborhood to which they moved in 1974. They had grown up together in southern California and were married after being separated long enough to earn degrees, he at Yale and she at Berkeley. They later traveled extensively throughout Africa and Europe as part of his assignment as an up-and-coming foreign service officer.

In Carderock Springs, Brad and Annette excelled in mixed doubles on the tennis court and Brad often took his sons and their friends on weekend trips for camping and skiing.

But after assignments in Ethiopia, Botswana and Italy, Bishop found the assignment at the main State building boring. And for the first time in his career, he was passed over for promotion, confessing to a colleague that the temporary setback had depressed him.

The charred bodies of Annette Bishop, her mother-in-law and three sons were discovered by a forest ranger in a shallow, burning grave in swampy, eastern North Carolina, after a fire tower operator thought she had detected a forest fire.

Despite skillful criminal and medical detective work, it was a week before the victims of that fire were identified. Even then, it took a bit of luck to make the connection with the missing Bishop family from suburban Washington, whose friends at first thought they had gone on one of their spur of the moment skiing trips.

The break came when agents of North Carolina Bureau of Investigation traced the purchase of a shovel that was used to dig the grave to Poch's hardware store in Potomac. By that time, the killer had a full week's head start and if that killer was Brad Bishop, as police charge, he had another two weeks before there was any hint of the escape route.

The Bishop's station wagon was recovered on March 18, 1976, in a remote campground of the Great Smokey Mountains national park, 400 miles west of where the bodies had been found. Campers told police the car had been parked there a week to 10 days before it became a focus of suspicion.

The evidence was clear that the car had been used to transport the bodies: The back floor was coated with dried blood on which police found blood-stained blankets, an ax and a shotgun. In the glove compartment were maps of the southern states and an empty vial of Sereaux, a drug similar to Valium that the FBI learned had been prescribed for Bishop by a psychiatrist he had been seeing.

For a while, the popular theory -- still believed by some -- was that Bishop walked into the half-million-acre park and became a victim of its famous brown bears.

The investigation that followed stripped away the privacy of the Bishop family and the facade of the ideal American family. Police learned of money trouble, of Annette Bishop's dissatisfaction with a life of travel, of the dominant role of Bishop's mother and Bishop's visit to psychiatrists. But police found nothing to help them understand what triggered that night of terror -- no extramarital affairs, no hidden cache of money and no prearranged plan.

The Bishop house on Lillystone Drive in Bethesda was sold four years ago. Today, children play in the long driveway, apparently unaware that the house was the scene of a mass slaying. Winters have blurred the new look of the stone entrance, which was torn up by police to get samples of the blood that dripped there as the killer carried the pajama-clad children and two women from the house to the stationwagon.

"Some day," muses police Cpl. Orbin, "my phone is going to ring and the caller won't be sending us on another wild-goose chase. It's going to lead us to Brad Bishop."