The often arcane testimony about child psychology was overshadowed by word from his attorney that Reiser, a 44-year-old computer engineer, probably will take the witness stand Monday morning to testify in his own defense against charges that he murdered his estranged wife Nina Reiser, who disappeared on Sept. 3, 2006.

Testifying as a defense witness, clinical psychologist Michael Fraga said he was "surprised and saddened" by the interview techniques used by Oakland police in interviewing Rory Reiser, who was 6 years old at the time Nina disappeared.

Those techniques could have improperly influenced Rory's recollection of what happened to Nina the last time he saw her, Fraga said.

On Wednesday, defense attorney William DuBois, said he wants to present "an affirmative defense" that Hans didn't have an opportunity to murder Nina based on Rory's previous testimony that she left Hans' house alive after she dropped off the children and kissed them goodbye.

But he said the prosecution's theory, on the other hand, is that "Rory was only six years old (when Nina disappeared) and is too little to believe."

Nina and Hans Reiser married in 1999 but had been separated for two years and were in the midst of a bitter divorce case and a battle over custody of their children when she disappeared Sept. 3, 2006.

Nina, who was 31 when she disappeared, was awarded legal custody of the children but Hans was allowed to have them several days a week.

The body of Nina Reiser, who was born and trained as a physician in Russia, has never been found, despite extensive searches in the Oakland hills and elsewhere. But Hans Reiser was charged with murdering her because prosecutors believe that DNA and blood evidence proves he killed her.

He has pleaded not guilty to the charges against him.

Rory and his sister Nio are currently living in St. Petersburg, Russia, with Nina's mother, Irina Sharanova.

Fraga said drawings Rory made that could be interpreted as showing Hans carrying Nina's body down the stairs of his house could have been influenced by Sharanova or others.

Alameda County Superior Court Larry Goodman didn't allow Fraga to talk about Rory specifically because Fraga never examined Rory.

But in response to a series of hypothetical questions posed by DuBois, Fraga said a boy who was 7 years old, the age of Rory was when he made several of the drawings, could have been influenced by relatives and others repeatedly telling him that his father had killed his mother.

Drawings done by such a boy could be "a product of what he was told instead of what he observed," Fraga said.

Fraga also criticized one of Rory's drawings as being "confused" and having "no direction."

Fraga said, "There's no readily-apparent theme" to the drawing.

Cross-examining Fraga, prosecutor Paul Hora took exception to Fraga's remarks, saying, "You have no idea what that kid went through" when his mother disappeared.

Hora also noted that a research paper Fraga cited as a source for his testimony in Hans Reiser's case says that having children do drawings can be a useful tool to make their memories more complete.

In addition, Hora got Fraga to concede that he has no idea if Rory told the truth during three days of testifying in his father's trial or if Rory has a good memory because Fraga has never examined Rory.

Before Goodman allowed Fraga to testify, Hora spent a long time questioning the psychologist's credentials.

Fraga admitted that Thursday was the first time he's testified as an expert in child cognition and that he served several years in federal prison for two felony convictions for possessing cocaine for sale.

Fraga said he also has convictions for forging U.S. Treasury checks, drunken driving and hit and run.

Fraga said that although he's worked in the psychology field for many years he has only been licensed since 2001.