"He was suffering from a psychotic state induced by the methamphetamine," said Dr. Alex Yufik.
Methamphetamine rushed through Thong Vang's blood when he walked into the jail, refused to follow orders, and then shot two correctional officers - Juanita Davila and Malama Scanlan - in September 2016.
Dr. Yufik has a model of a brain in his hand to show jurors how he says meth affects the system — flooding the brain with high amounts of dopamine.— Corin Hoggard (@corinhoggard) March 26, 2018
He says Vang was in a meth psychosis when he shot officers Juanita Davila and Malama Scanlan in September 2016.@ABC30 pic.twitter.com/lvq7Z1kYdx
The forensic psychologist who saw him a few months later says the drug made it so Vang couldn't control his behavior.
"When you change a person's biology, their behavior also changes," Dr. Yufik said. "In this particular case, he started to experience psychotic symptoms."
Dr. Yufik says meth has extreme effects on the yellow parts of his model brain -- the limbic system and the amygdala, which regulates behavior. He says Vang's voluntary intoxication heightened his antisocial personality disorder and made him paranoid.
"He started to believe that people were after him, that people were trying to kill him, actually kill him, that people were trying to steal secret files from his phone," the psychologist said.
Dr. Yufik made the argument for meth psychosis once before in Fresno County, back in 2013. In that case, a jury didn't buy it and convicted Daniel Galvan of first-degree murder despite his meth use.
Vang told the doctor he started using meth when he was in prison on a 1998 rape case.
Yufik admits Vang suffered from the antisocial personality disorder even before he went to prison and noted that even a sober Vang has violent tendencies.
"He suffers from abrupt mood changes that can turn violent?" prosecutor William Lacy asked.
"Yes," Dr. Yufik replied.
"He holds grudges against those who have transgressed him in the past?" Lacy asked.
"Yes," the doctor responded.
"Getting even with those who he perceives as having wronged him can be a major preoccupation?" Lacy, the prosecutor, asked.
"Yes," Dr. Yufik said.
Attorneys finished presenting evidence Monday and they'll make their closing arguments Tuesday.
Legally, jurors can find a defendant not guilty -- or guilty of a lesser crime -- if they believe intoxication kept the person from forming the intent, but legal experts say it's a hard argument to make when the intoxication is voluntary.
Vang faces more than 100 years to life if the jury convicts him on all the charges.