As Paul M. Johnson Jr., 49, was held under a death threat in Saudi Arabia, his family gathered in New Jersey on Wednesday and issued a plea for his terrorist captors to release him.

"We just ask that they treat him with dignity and respect," Donna Mayeux said of her brother, during an interview with CNN. "Just please, please don't murder him."

A group calling itself al Qaeda in the Arabian Peninsula kidnapped Johnson from his home Saturday in Riyadh, Saudi Arabia. The group released a videotape Tuesday of a blindfolded man, who said he was Johnson and stated his occupation. The group said it will execute Johnson within 72 hours -- as early as Friday -- if the Saudi government does not release jailed al Qaeda detainees.

The tape, posted on an Islamic fundamentalist Web site, showed a hooded man holding an AK-47, who is believed to be Abdulaziz Muqrin, al Qaeda's leader in Saudi Arabia. The group previously claimed a "legal right" to treat hostages "the same way they treat our people" in a reference to the abuse of Iraqi prisoners by U.S. troops.

U.S. officials have said the posting is credible and that they are taking the threat seriously. Saudi officials have said they will not negotiate with terrorists and have warned that the kingdom plans to deploy more soldiers.

Johnson, described by friends as a technically proficient man with an abiding respect for Saudi culture, has lived in the desert kingdom for more than a decade. He is employed by the defense contractor Lockheed Martin Corp. and works on Apache helicopters.

He grew up in nearby West Creek Township, a tightly knit working-class town on the Jersey shore. His home town, just north of Atlantic City, is decked with yellow ribbons strung along power lines and on fences and in strip malls. Neighbors planned a prayer vigil for Thursday night, and friends recalled Johnson as a typical working-class kid, a boy who expected to work hard for a living.

"He's an ace when it comes to electronics," said Sam Sprague, 49, who attended high school with Johnson. "Once he turned a transistor radio into a beeper. He used to drive the librarian crazy with it."

Johnson's 67-year-old mother, who is ailing, lives with Johnson's brother in a trailer park in nearby Stafford Township. Johnson's son, Paul Johnson III, traveled Tuesday from his home in Florida to New Jersey. He went on CNN on Wednesday, with his 3-year-old son, to plead for his father's life.

"He's been there for over 10 years, and he likes working with the Saudis," Johnson said. "He respects their culture . . . he respected everything they believed in."

The family had hoped to reunite for the first time in several years in Thailand next Christmas. Johnson, married to a Thai woman who has remained in Saudi Arabia, is building a vacation home there.

Johnson's son has been in touch with his stepmother. He said: "She's waiting for my father to come through the front door. It's very hard for her being so far -- and we're here. I'm thinking about her constantly."

Johnson pointed to his son, Paul Marshall Johnson IV, and spoke of his optimism that his child might yet see his grandfather. "Please let him come home and be a grandfather," Johnson said on CNN.

Researcher Meg Smith in Washington contributed to this report. Powell reported from New York.

In a message posted on an Islamic fundamentalist Web site, this man identifies himself as Paul M. Johnson Jr., an employee of Lockheed Martin Corp.This undated photo shows Paul Johnson and his wife, Noon, who is from Thailand but who has remained in Saudi Arabia. A poster and a yellow foam ribbon near the home of Paul Johnson's sister near Tuckerton, N.J.