Kidnap victim Elizabeth Smart stormed from a Utah courtroom Wednesday as a psychiatrist testified that her alleged attacker had been motivated by a desire to have children and create a new race in an imaginary Zion.

Forensic psychiatrist Paul Whitehead took the witness stand under subpoena during the federal trial of former street preacher Brian David Mitchell on kidnapping and other charges.

Whitehead, who was subpoenaed to testify by the defense, said he gleaned this information from the journals of Wanda Eileen Barzee, Mitchell's estranged wife, and police reports.

Whitehead said Mitchell and Barzee had been caught shoplifting baby clothes and that they had chastised Smart for saying she did not want to have children.

"Mr. Mitchell was talking with Miss Smart about having babies to the point where Miss Smart actually picked out a name in case that happened," Whitehead said.

At that point, a visibly angry Smart got up from her seat in the front row of the courtroom and left to a private area. Her mother followed. They both returned to the courtroom about 30 minutes later.

The remarks came as Whitehead explained some of the odd characteristics or red flags he said he saw when trying to determine whether Mitchell suffered from mental illness.

Prosecutors, who believe Mitchell is faking mental illness to avoid prosecution, later tried to diffuse the remarks by noting that Barzee wrote her journals during a period of time when she was suffering an untreated mental illness.

Whitehead is one of more than nearly two dozens witnesses defense attorneys have called seeking to build an insanity defense. Attorneys don't dispute the facts of the case, but contend that because of his mental illness, Mitchell can't be held responsible for the crimes.

If convicted of the charges, the 57-year-old street preacher could spend the rest of his life in prison.

Whitehead, is a staff physician at the Utah State Hospital, where both Mitchell and Barzee were incarcerated after being found incompetent for trial in parallel state cases. Mitchell was at the Provo hospital from 2005 to 2008, when federal prosecutors took over his case.

Whitehead believes Mitchell suffers from a major psychotic illness and diagnosed him with a delusional disorder — a condition he described as holding "a false belief based on incorrect interpretations about external realities and that are firmly maintained" despite a lack of supporting evidence."

The tricky part of such disorders, however, is that they typically manifest only in one area of a person's life, Whitehead said. So Mitchell exhibits delusions related to religion, but seems otherwise normal in other aspects of life, said the doctor, who spent nearly five hours on the stand.

"These guys can be highly functioning, highly manipulative and it's not so much the belief, but what they are doing with the belief that's important," he said.

Whitehead said he believed Mitchell's disorder led him to routinely confuse coincidence with "confidence that God is providing for him."

Earlier witnesses, including both Smart and Barzee, have said Mitchell was insincere in his beliefs and that he used religion to manipulate others. Whitehead said he didn't believe manipulation alone could explain what Mitchell had done and that he seems very emotionally committed to his beliefs.

Cook also tried to dilute the impact of Whitehead's assessment of Mitchell's by comparing the hours he spent evaluating Mitchell to Smart's nine months in captivity.

Whitehead said he had only spent about 32 hours in direct contact with Mitchell and conceded that none of it came during the nine months Smart was missing — from June 2002 to March 2003.

Mitchell was again removed from court Wednesday for disrupting the proceedings by singing hymns. He watches the trial from a holding cell on a television. On Tuesday, he was taken out on a stretcher by paramedics after suffering an apparent seizure. He spent several hours at a hospital before being returned to a jail.

The trial is in its fourth week and expected to last until Dec. 10.