Two separate slayings with a shockingly similar theme have played out in the Sonoma County courts recently, although experts maintain the brutal crimes remain a rarity nationwide.

Parricide — the act of killing one's mother or father — was a factor in the case of Houston Herczog, the 22-year-old Santa Rosa man found not guilty by reason of insanity last week in the slaying of his father.

It's also a critical detail in the stabbing death of a Sebastopol woman earlier this year, allegedly at the hands of her adult daughter, Julia Franzen, 24.

Despite resemblances between the two killings — which happened about 15 miles and two years apart — parricide accounts for only a fraction of all homicides across the country.

The most recent FBI statistics covering a 25-year period show that just 2 percent of all slayings were either patricide or matricide.

But in the rare times when children kill their own parents, people take notice.

"It's a very small number of people who do this," said Dr. Sara West, a forensic psychiatrist at Case Western Reserve University in Cleveland. "They make headlines because it's unusual."

Aside from Herczog and Franzen, there have been few Sonoma County cases in recent years that are alleged to involve parricide. But they are not unheard of.

Dennis Hughes, 41, of Rohnert Park, beat his mother to death with a baseball bat last year after she forced him to move out of their house. He was shot to death by San Francisco police. And in 2007, Ezra Hoyt, then 33, also of Rohnert Park, was charged with stabbing his mother to death with a 45-inch sword. Hoyt was diagnosed with paranoid schizophrenia.

West, who has conducted dozens of sanity evaluations for the courts, said perpetrators tend to be young men who, like Herczog and others, have been diagnosed with schizophrenia. They are generally single and living at home, often with their mothers, West said.

Their mothers are their most common target. Guns are the weapon of choice, although knives are not uncommon, in part because they are so easily accessible, she said.

"Stabbing is a very intimate crime," said West. "It conveys a lot more emotion ... and speaks to the level of conviction."

An autopsy showed Herczog stabbed his father, Mark Herczog, 63, with several kitchen knives at least 60 times. Many of the wounds were to his face and neck. And he appeared to try to sever his father's head with a bread knife.

Franzen is also accused of stabbing her mother multiple times. Police said evidence suggests she chased Nancy Franzen, 59, through her house, attacking her with a knife, before she collapsed.

Julia Franzen, who has since been deemed mentally unfit to stand trial, was sent to Napa State Hospital this week for treatment.

Those who kill their parents can have several motives and range in age from children to adults. Kathleen Heide, a professor of criminology at University of South Florida and author of a book on the subject, describes four types of killers.

There are severely abused children who kill to end the abuse. They tend to be minors. Another type is the mentally ill person who hears voices and has delusions his or her parents are out to get him or her. Testimony in the Herczog trial suggested he thought his father was possessed by an evil force.

Heide said another type is the dangerously anti-social person who kills Mother or Father for money or freedom to date someone, for example.

A fourth type is an enraged person who erupts in violence because of drugs or alcohol.

"Parricide is very, very uncommon," said Heide, who has studied it for three decades.

Drug use, which was alleged in the Herczog slaying, can make it difficult to determine where the effects of controlled substances end and mental illness begins.

Prosecutors in Herczog's case tried to highlight his use of the prescription stimulant Adderall to counter evaluations by three psychiatrists who believed Herczog was schizophrenic.

In the end, Herczog prevailed in convincing jurors that he didn't have the capacity to determine right from wrong.

That in itself is unique, according to West. She said the sanity defense is only used in about 1 percent of criminal cases, and it's usually not successful.

"It often comes down to a battle of experts," West said. "They take the stand and whoever is more convincing is going to be persuasive to the jury."

Santa Rosa criminal attorney Chris Andrian said he doesn't see the recent Sonoma County cases as evidence of a trend. He said it is mere coincidence that two similar cases are going through the courts at the same time.

But he said they do point up a problem — the lack of mental health services for people on the verge of a psychotic break.

"Seems like the only way you can get mental health treatment is to commit a crime," Andrian said. "I think you're going to see more people in the criminal justice system with mental issues. The services just aren't there."