Lawyers say the boy's father, Hans Reiser, was engaged in a bitter custody dispute with the 43-year-old Nina Reiser at the time she disappeared.
She disappeared after dropping off the boy, Rory, and his younger sister at the home of her estranged husband last year. Her body has never been found, leading the defense to speculate she could even be living in her native Russia .
Rory, who has previously given conflicting statements about what happened, was vague Tuesday about what happened the last time he saw his mother.
At a preliminary hearing last year, Rory testified he said goodbye to his mother and saw her leave the house.
Tuesday, he said he did not remember what happened after his mother said she was leaving.
Rory said he went to the house with his mother and sister, ate macaroni and cheese fixed by his father and then went downstairs with his sister to play computer games.
The boy, who has been living with his maternal grandmother in Russia for several months and spoke with a slight Russian accent, at times gave very precise answers. But on other details he was unsure.
He was clear that he has not seen his mother or gotten a phone call or letter from her.
"Do you have any idea where she is?" asked prosecutor Paul Hora.
"No," Rory said.
"How do you feel about that?"
Outside the courtroom, defense attorney William Du Bois said his client was "experiencing anxiety."
Du Bois, who expected to begin cross-examining Rory on Wednesday, questioned why the boy's story has changed.
"Now, suddenly, after one year of talking to the people in Russia, he doesn't remember anymore," he said.
"They influenced him," Du Bois said. "He's been to psychiatrists; they've been talking to him. They've got him completely hating his father."
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