Chu said Rockefeller, whose real name is Christian Karl Gerhartsreiter, was not suffering from delusions and knew it was wrong to take his daughter. He said he based his opinion in part on evidence that Gerhartsreiter planned the kidnapping for months and later tried to conceal it.
"I couldn't find anything other than that he is responsible for whatever criminal activity he is charged with," Chu said.
He added, "I felt that he clearly understood the wrongfulness of his conduct."
That conclusion is opposite what defense experts said: that Gerhartsreiter's mental health problems are so severe, he isn't responsible for actions.
Prosecutors claim that the German-born Gerhartsreiter, 48, is a con man who has told countless lies about himself since moving to the United States as a teenager in 1978.
He is accused of taking his daughter seven months after losing custody of her to his ex-wife, Sandra Boss, a partner in the London office of the management consulting firm, McKinsey & Co.
Authorities say he pushed a social worker who was overseeing the father-daughter visit to the ground, then fled in a waiting car with a driver he hired.
On Monday, jurors are to hear closing arguments from prosecutors and defense attorneys and to begin deliberating.
Chu said he diagnosed Gerhartsreiter with a "mixed personality disorder" with narcissistic and anti-social traits.
But he rejected the defense claim that the elaborate stories he told about his past and his use of multiple aliases - including the famous Rockefeller name - were prompted by mental illness. Chu said the fanciful stories he told were "creations" and "deliberate fabrications," not delusions.
Witnesses have testified that Gerhartsreiter claimed an aristocratic background and told a wide variety of stories about what he did for work, describing himself at varying times as a cardiovascular surgeon, a physicist, a ship's captain and a member of the Trilateral Commission, a private organization established in the 1970s to foster cooperation between the United States, Europe and Japan.
Chu said that Gerhartsreiter's answers in a 28-item questionnaire he gave him indicated "a certain amount of exaggeration of symptoms."
For example, Chu said, when asked how often he found himself in places and had no idea how he had gotten there, Gerhartsreiter said 70 percent.
"I did not find that credible," Chu said. If it were true, Gerhartsreiter would have trouble even functioning, Chu said.
During cross-examination by Gerhartsreiter's lawyer, Chu acknowledged that he did not diagnose Gerhartsreiter with malingering, or faking.
He also acknowledged that he had almost no experience in forensic psychiatry and spent just 2½ hours interviewing Gerhartsreiter, compared with the 12 to 16 hours spent by the defense experts. He also could not give a complete answer when asked how mental disease is defined under Massachusetts law.
The two defense experts both said they diagnosed Gerhartsreiter with delusional disorder, grandiose type and narcissistic personality disorder.
Dr. Keith Ablow, a psychiatrist from Newburyport who has written fictional books and appeared on numerous television shows, testified Wednesday that Gerhartsreiter told him his father was emotionally abusive during his childhood, calling the boy "human refuse."
On Thursday, Ablow said Gerhartsreiter told him his father gave away his musical instruments and "openly questioned" whether the boy "might be a homosexual." His father also asked his mother, in front of the boy, whether he was really his son, Ablow said.
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