Almost four decades have passed since anyone saw William Bradford Bishop, Jr.
That last sighting was March 2, 1976 -- one day after police say he murdered his wife, three sons and his mother in their Potomac, Md. home.
Pictures of the State Department employee were splashed on TV screens and newspapers across the country in the years that followed -- yet, even today, this suspected killer remains missing.
"It's getting late in the day for him," FBI Special Agent in Charge Steve Vogt told the News 4 I-Team. "He's 77, but we're going to put it out there and give it our best shot."
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Vogt fought to have Bishop added to the agency's Ten Most Wanted list because he thinks Bishop might be living in plain sight.
"His wallet has never been found. His passport has never been found," Vogt said. “There's no indication that he's dead."
But with so much time passing, what would Bishop look like and be doing today?
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The FBI said the most notable feature is Bishop's pointed chin. But he also has a flaw to his upper right lip that sometimes curls up when he smiles. Both could be hidden with facial hair.
He also has a scar on his lower back from surgery.
Vogt said, “I would expect him to still be in fairly good shape, based on his activities and what he enjoyed doing."
Old home movies recovered by the FBI show Bishop loved the outdoors, even as a kid. He was described as athletic and adventurous, often camping, hiking and skiing and especially fond of the Sierra Nevada Mountains in California. His military background made him self-sufficient in the elements.
Bishop's other passion? His dog Leo.
"People brought it up over and over that he loved his dog,” Vogt said. “He took his dog with him. That's the only creature that survived in that house."
Vogt said it's likely Bishop would still own a dog, possibly even the same breed, a golden retriever.
Bishop had a pilot’s license. Investigators said he might still ride a motorcycle, something he enjoyed doing back in the seventies when he used it to get to work each day at the State Department.
The State Department’s Special Agent Carlos Matus said, “He was educated. He spoke several languages fluently."
Those languages included Italian, French, German and Croatian.
But Matus said Bishop’s personality could be volatile. Coworkers described him as a perfectionist, having a temper and quick to anger.
"Bishop was an arrogant man,” Matus explained. “He tended to overreact sometimes explosively to minor things."
Bishop's job as a foreign service officer involved making passports, leading many to wonder if he could have traveled overseas. There have been a number of unconfirmed sightings over the years in Europe.
"There's a certain potential that he could be overseas,” Matus said. “He was certainly trained for that. He was certainly educated enough to pass off as a diplomat."
But Vogt points to another, similar case, as a more hopeful scenario. John List, a New Jersey man convicted of killing his entire family in 1971, was found 18 years later in Richmond, Va.
When we asked if Bishop could be married or have kids, Vogt said, “I believe so. John List remarried under the new name Bob Clark. He had a new wife. It's quite possible."
A 40 year old mystery, investigators hope could finally be solved with one phone call.
As Vogt explained, "I think people are reluctant to call. They think that couldn't be him. There's no way my neighbor or my dad is that guy. But he can be. He can be anywhere in this country right now."