OAKLAND, Calif. -- An Alameda County prosecutor, attempting to prove an East Bay man murdered his estranged wife and then hid her body, unveiled plans Wednesday to call the couple's 8-year-old son to the witness stand to testify against his father.

Reiser, 43, is charged with killing his estranged wife, Nina Reiser, who vanished after dropping off the couple's two children at Hans' home last fall.

Nina's body has never been found, leading the defense to question whether she is even dead. But prosecutors say circumstantial evidence shows she was murdered.

A murder weapon hasn't been found but on Wednesday, prosecutor Paul Hora, continuing his opening statement for a second day, said Reiser has a black belt in judo and suggested he could have strangled Nina.

The prosecutor built up a detailed description of the day Nina went missing, including showing a snippet of grocery store video footage he identified as Nina and the children leaving with a cart full of goods just before going to Hans' home.

At the defense table, Hans turned toward the screen as the video played, watching intently as the children moved in and out of view.

The groceries were later found rotting in the back of Nina's abandoned minivan when it was discovered some days after she went missing.

The couple's son, Rory Reiser, was six when Nina disappeared and may offer confusing testimony because he has given conflicting statements in the past about what happened, the prosecutor said.

"He's just so little and so small, he's not reliable," Hora said. The prosecutor also suggested that Hans may have influenced the boy.

But Hora said he wants jurors to decide for themselves what weight to give the testimony.

The boy and his younger sister have been with their maternal grandmother in Russia for some months.

At a hearing last December, the boy testified he saw his mother drive away after dropping the children off.

The judge presiding over that hearing asked Rory to return for further testimony, but his maternal grandmother, who had taken the children back to Russia for the holidays, did not return him to court.

Hora said Wednesday the grandmother had consulted with therapists and other experts who agreed it wasn't in the child's best interests to return.

As for Hora's reservations about the boy, defense attorney William Du Bois said outside court, "he doesn't want Rory to be reliable because Rory testified unequivocally at the preliminary examination that on the last day he saw his mother, she gave him a hug, she walked out the door -- he described it, very detailed description -- walked up the stairs got in her car and drove away, thereby depriving his father of any opportunity to commit this crime."

Hora was expected to continue his statement Wednesday and possibly Thursday morning, after which Du Bois was expected to address the jury.