A 22-year-old Santa Rosa man stabbed his father dozens of times in the face, neck and torso before lofting a guitar amplifier over him and slamming it down on his head, a prosecutor said Monday.

Houston Herczog killed Mark Herczog, 63, in the 2011 attack in the kitchen of their Rincon Valley home, prosecutor Bob Waner told jurors at the opening of Herczog's trial.

The slaying was witnessed in part by Herczog's 17-year-old sister, Savannah, who was awakened by her father's "death cries" and saw her brother holding a knife, Waner said.

Officers responding to her frantic 911 call arrived in time to find Herczog emerging from the kitchen, his hands covered in blood, an officer said.

Herczog admitted the slaying, lay down on the floor and surrendered, Santa Rosa police Officer Brandon Matthies testified.

"He said, 'I killed him,' " said Matthies, who watched Herczog from the front door of the Parkhurst Drive house.

The details came in the first day of trial for the 2009 Santa Rosa High School graduate charged with murdering his father.

He has pleaded not guilty by reason of insanity. His lawyer, Deputy Public Defender Karen Silver, maintains the killing happened during a psychotic break.

Family members report Herczog was suffering mental health issues in the period leading up to the attack. Three doctors, including two appointed by the court, diagnosed him with schizophrenia.

A fourth doctor hired by the District Attorney's Office contends Herczog was in a drug-induced psychosis from taking Adderall, a stimulant prescribed to his mother.

If he is convicted of murder, a second trial will be held to determine whether he was sane at the time of the attack. If jurors say he was, he faces up to 25 years to life in prison.

A finding of insanity could put him in a mental hospital for many years.

Both sides estimate the first phase of the trial will be over in a few days.

Prosecutors are not expected to call Savannah Herczog as a witness.

Herczog's lawyer will put doctors on the stand during both phases. She also intends to call Herczog's aunt, Annette Keys, who was visiting from Ohio before her brother was killed. Herczog's mother, Marilyn Herczog, is not expected to testify.

In her opening Monday, Silver challenged prosecutors to find a motive other than insanity. She said Herczog was not capable of premeditation and suffered from delusions that his father was possessed by an evil spirit.

Herczog, who has been in jail since the November 2011 killing, stared down at the defense table through most of Monday's testimony, which included the playing of a 911 recording with his sister's voice on it.

He appeared to show no emotion when she screamed her father was dying or when prosecutors displayed pictures of the blood-stained kitchen floor with his father's torn shirt on it.

You can reach Staff Writer Paul Payne at 568-5312 or paul.payne@pressdemocrat.com