Alameda County Assistant Public Defender David Klaus said the psychiatrist interviewed One Goh and several of his relatives and determined that Goh, 44, suffers from paranoid schizophrenia that dates back several years.
The condition is so deeply rooted that it causes Goh to distrust people, including those trying to help him.
"He's got a deep and fixed delusional system. It's based in religious beliefs around the battle between God and Satan and his role in that battle," Klaus said about Goh. "He's deeply paranoid and trusts no one. I think this condition is really central to this entire story."
A judge last month ordered the evaluation from two psychiatrists after Klaus said Goh refused to speak to him. A second psychiatric evaluation has not occurred, Klaus said.
Goh is charged with seven counts of murder and three counts of attempted murder in the April 2 attack at Oikos University in Oakland.
He has pleaded not guilty to killing the six students and receptionist that became America's deadliest school shooting since the 2007 attack at Virginia Tech.
Authorities said Goh, a former Oikos student, planned the killing spree at the school that caters to Korean immigrants after becoming angry with school officials over a tuition dispute. He previously decided to drop out of the school's nursing program.
If a second psychologist finds Goh incompetent, then it's likely he will be sent to a state mental hospital to undergo treatment, Klaus told reporters after Monday's brief hearing. Doctors can then force Goh to take medicine and attempt to prepare him for an eventual trial.
Klaus said that he and his co-counsel still have trouble talking with Goh because of his mental state.
"I have felt very strongly since the beginning of the case that he is severely mentally ill that he has been dealing with this for most of his life and caused him all kinds of difficulties along the way," Klaus said.
"I believe that mental illness was, if not the direct cause, certainly a massive catalyzing factor for this terrible tragedy that he committed," Klaus added.
Klaus said that he finds the psychiatrist's report "very strong." He said the mental health expert also examined Goh's videotaped confession to police and reviewed hundreds of pages of police reports.
Klaus said he expects to receive a second psychiatric report by the time Goh is due back in court Jan. 7.
He said that he and the Alameda County district attorney's office will decide if Goh should be sent to a state mental health facility or whether a trial on Goh's mental health will be conducted.
"He's in a state of deep isolation, depression and shame," Klaus said. "He's in pretty bad shape."
The husband of one of seven victims killed isn't buying Goh's schizophrenia.
Efanye Chibuko, whose wife, Doris Chibuko, 40, was killed at the school, said after Monday's hearing that Goh is knew exactly what he was doing on that fateful day.
"I believe he is acting," Chibuko, 42, said. "I don't believe him. He's just playing the (legal) system."
Chibuko said his wife would tell him that she and other classmates were fearful of Goh. Now, Chibuko said he's a widow comforting his four children mourning the loss of their mother.
"I hope the system doesn't let him get away with it."