Family Brainwashed by Dad Struggles to Heal

July 6, 2010— -- The San Joaquin Valley in central California is one of the world's most productive agricultural regions. It's an arid desert irrigated to make a land of plenty, where crops such as grapes and garlic are grown.

But on March 12, 2004, the city of Fresno was stunned by the revelation that the devil had seemingly sowed his seed in their midst.

What started out as a routine custody dispute at a house in the west-central area of the city suddenly and inexplicably escalated into the worst mass murder in Fresno's history.

Nine people were found dead inside the house, their bodies piled in a back room. In the tangled heap, there were two adults and seven young children -- three of whom were under the age of two.

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Police arrested 57-year-old Marcus Wesson, who emerged from the residence with blood on his clothes. Neighbors' accounts led police to believe that Wesson controlled his family in a cult-like manner, and that he possibly had fathered several of the deceased children with his own daughters and nieces.

Two of those nieces had come to the house to get their children, which ended up triggering the mass murder.

But several of Wesson's surviving sons rose to his defense, telling reporters that that Wesson was a wonderful father who loved his children and never could have hurt them.

Exactly how the purported "wonderful father" also could be one of the most deranged monsters in American history is the strange question at the heart of this story.

CLICK HERE to see photos of the Wesson family and photos from the day of the massacre

The answer lay in Wesson's extraordinary power to control the minds of his wife and children. It seemed to be a power that placed him in the company of such madmen as David Koresh, who led his followers to their fiery death at Waco, Jim Jones, whose flock committed mass suicide in Guyana, and of course, Charles Manson, who turned flower children into random killers.

Wesson was all of this, and more. To help understand how he was able control his family so completely, "Primetime" sat down with Wesson's wife Elizabeth Wesson and five of his surviving children.

Wesson's sons -- Adrian, Serafino and Dorian -- told ABC News correspondent Jay Schadler that only now, years after the crime, could they see their father for what he was: psychotic, delusional and narcissistic.