Seattle true crime writer Ann Rule has written about killers for 35 years. She's the author of dozens of books detailing the evil crimes of serial killers, spree killers and murderers who kill their own family members. Rule thinks Josh Powell's crimes rank among the worst.

"This would be in the top five things that have shocked me over the last 30 years," said the former police officer. "A lot of parents kill their children to get revenge on an ex-spouse but they usually don't die themselves."

Revenge is a classic motive for murder. Control is another. After Susan Powell disappeared from her Utah home, friends and family complained that Josh Powell had been controlling in the marriage.

With his wife out of the picture, Powell sought to control his children.

"And by golly, they are there for this type of parent to do what they want with and it was sort of a twist on the husband who kills his wife [saying], 'If I can't have you, nobody can,'" said Rule. "I own them."

Powell lost a large measure of control when his wife's parents, Chuck and Judy Cox, were awarded custody of his kids last fall when Powell's father was arrested on charges of possessing child pornography and voyeurism.

"He hated Chuck and Judy Cox and he'd be damned, I think, if he would let them have his little boys," reasoned Rule.

So murder-suicide was Powell's ultimate power play.

"Things were closing in on Josh Powell and the boys were becoming more verbal and they were very smart and remembering things and I think he wanted to maintain control over his life and this was why he decided to take his own life because that still gave him that last control," explained Rule.

It's not uncommon. Researchers calculate that parents kill their children 250-to-300 times each year in the United States. What's known as filicide is the third leading cause of death among children between the ages of 5 and 14, according to F.B.I. crime statistics.

In April 2009, a few months before Susan Powell disappeared from her home in Utah, a Graham, WA man shot and killed his five children and then killed himself. Investigators say James Harrison had learned that his wife was leaving him. It's another example of a controlling man who was losing control.

Rule is the author of "Stranger Beside Me," the story of Ted Bundy and "Green River Running Red" about the Green River Killer, Gary Ridgway. She's also written about Diane Downs, the Oregon mother who killed her two small children, in the book "Small Sacrifices."

Rule is researching a book about the Susan Powell case with the approval of the Coxes. She doesn't think Powell was crazy or psychotic. Like many of her subjects, she thinks Powell was a sociopath who saw himself as the center of the world, with little concern about others, even his own family.

Tim Haeck, 97.3 KIRO FM Reporter

You might also be interested in:

• Latest developments in Josh Powell case
• Autopsies: Powell's sons suffered chop injuries
• Interview with grandparents of Powell boys
• David Boze: The Powell boys didn't want to go