06/08/2004 at 08:00 AM EDT
In a surprise disclosure at the trial of double-murder suspect Scott Peterson on Monday, Sharon Rocha, mother of Laci Peterson, for the first time publicly disclosed that she had become so disenchanted with the elusive behavior of son-in-law Scott that she secretly allowed Modesto police to tape record her phone conversations with him.
"It was his behavior that he didn't show the concern about the fact that Laci was missing," she testified on the stand. "Also, I felt I would schedule meetings with him and he would always cancel them. I thought he tried not to be alone with me."
Prosecutors allege Peterson, 31 – who was having an affair with massage therapist Amber Frey – killed his eight-months-pregnant wife in their Modesto home, then drove Laci's body nearly 100 miles to San Francisco Bay and dumped it from his small boat. He has pleaded not guilty.
Rocha at times fought back her tears during more than three hours on the stand and described the numerous occasions in which she tried to sit down with her son-in-law.
"It was suspicious," she said, explaining that he was always out hanging posters of her missing daughter. "There were many times at the volunteer center that we would miss each other. It was so wrong behavior."
When the Modesto police approached her about taping her phone conversations with Scott, she agreed. The police never asked her to ask him specific questions, but on the Feb. 15 recording played in the courtroom, the petite blonde grilled Scott relentlessly for details about the days beginning Dec. 24, 2002, when Laci first went missing.
Questions concerned such topics as the clothes Laci was wearing when he last saw her. Peterson replied that she was wearing a white top and black pants. But when asked what kind of shoes Laci was wearing, he said he didn't know. That's when Rocha snapped, "Don't you know what shoes she was wearing?"
She also questioned him about his plans for Christmas Day.
She went on to ask him whether Laci was wearing his blue pajamas on the night of the 23rd, and about his not smelling any cooking at the house when he got home from fishing – since Laci was planning on baking gingerbread for Christmas.
"This is odd that you didn't notice anything when you walked into the house and took a shower," she said.
For the defense, Scott's attorney Mark Geragos attempted to counter the testimony about Rocha's suspicions, pointing out that Laci's sister Amy Rocha said she told police that her brother-in-law "was the last person who would ever harm anyone."