ROMULUS, N.Y.—When Levi Karlsen was crushed to death while fixing up a pickup truck four years ago, authorities in his quiet county thought it was a sad mishap. But now they say his death was no accident: His father has been charged with murdering him for insurance money.

Karl Karlsen, who initially told police he'd found his son's motionless body trapped under the truck, was being held without bail Saturday in the Seneca County jail in New York's Finger Lakes region. The 52-year-old father was arrested Friday after an eight-month reinvestigation of a death that had long since been ruled an accident.

The case also is prompting a new look at a 1991 California fire that killed Karlsen's first wife.

The family's phone wasn't accepting messages Saturday, and jail officials didn't know whether Karl Karlsen had a lawyer.

Levi Karlsen, 23, died in November 2008 while working on a truck in a barn on the family's property in Romulus, about 55 miles southwest of Syracuse. A distraught Karl Karlsen told sheriff's deputies he had returned from a family event and found the truck had toppled off a jack and trapped his son underneath.

"There were no indications of foul play, and from all signs, this appeared to be a very tragic accident," Seneca County Sheriff Jack Stenberg said in a press statement.

But then, this March, the sheriff's office learned about a life insurance policy on Levi Karlsen, taken out just days before his death, with his father as sole beneficiary. Investigators took another look at the circumstances surrounding the alleged accident and concluded that Karl Karlsen made the truck fall on his son, went to the family gathering and returned to make a show of supposedly discovering his son's body, Stenberg said.

"To think that a father could cause a vehicle to fall off a jack, crushing his son, and then leave for four hours—knowing all the time that his son was pinned under the truck, apparently dead—is unconscionable," the sheriff said.

He said his office and other authorities were now looking into the 1991 blaze that took the life of Christina Karlsen, the defendant's first wife. The sheriff's office declined to give further details Saturday.

She was killed in a New Year's Day fire that engulfed the couple's home, her father, Art Alexander, told The Post-Standard of Syracuse on Saturday. He said his former son-in-law told investigators he'd been in the garage when the blaze began.

Karl Karlsen said he managed to rescue Levi, then 5, and the couple's two other children by pulling them to safety through a bedroom window but couldn't get to his wife, Alexander recalled. He said Karlsen ended up with $200,000 in insurance money and used it to buy the property in Romulus.

Alexander told The Post-Standard he always had questions about the fire but was afraid he'd be cut off from his grandchildren if he broached the subject with Karlsen.

"Just to keep it bottled up—it was the hardest thing I ever did in my life," he told the newspaper.