A 78-year-old man who died after setting a fire to hide the murders of his third wife and her brother had killed two previous wives, a sheriff says.

Everette Simpson had served a total of 20 years for the two killings.

He spent nine years in a California prison for second-degree murder of his first wife, who was hacked 16 times with a butcher knife in 1960, and 11 years in Louisiana for manslaughter of his second wife, attacked with knife and hatchet and then smothered with a pillow in 1983, authorities said.

He died of smoke inhalation April 3. Estelle Simpson, 69, and her brother, Allen Martin, 75, were bludgeoned in their sleep.

"This is incredibly frustrating for people who spend their careers chasing these monsters," St. Tammany Parish Sheriff Jack Strain said Friday. "Everyone deserves a second chance, but when you start letting out cold-blooded murderers not once but twice, you've got to wonder what's going on."

Simpson was charged in 1960 with first-degree murder of Virginia Hudson, 35, in Los Angeles, and was convicted of second-degree murder, Strain said. He pleaded guilty in 1983 to manslaughter of Ruby Richardson in Shreveport, the sheriff said.

"We know he committed at least three horrible murders," the sheriff said. "I don't know if that qualifies him as a serial killer, but there's certainly the possibility that he killed others that we don't know about."

The Simpsons had been married for 10 years.

Martin's and Estelle Simpson's relatives were stunned by word of the previous convictions.

"Why in the world was he walking the streets as a free man? That's utterly unbelievable," said Earl Martin Sr., a cousin who lives in Lanham, Md. "It's absolutely beyond my comprehension."

Relatives said Simpson was upset that his brother-in-law had moved in with them about a year ago after he suffered a stroke and had to start using a walker.

Strain said it's unclear whether that precipitated the killings.

"We know he already had a clear pattern of forming relationships with women and then killing them," Strain said. "His actions may have been driven more by something in his psychological makeup than any specific problems with his wife."