Jackie Peterson said Thursday it's not surprising that a man found concrete dust in the bottom of her son Scott Peterson's boat.
The residue was likely there because of the boat's concrete anchor, she said. "It was mentioned long ago that Scott had a cement anchor."
Scott Peterson's wife, Laci Peterson, was reported missing Dec. 24. Scott Peterson told police he last saw her at 9:30 a.m. as he left with the boat to go fishing in the Bay Area and she prepared to walk their dog in East La Loma Park.
Jackie Peterson was responding to comments made by Bruce Peterson during a television interview. He sold the boat to Scott Peterson in December. They are not related.
Detectives asked Bruce Peterson to look at the boat after police seized it.
Since Laci Peterson's disappearance, hundreds of officers and volunteers have searched from Tuolumne County to the Berkeley Marina for the missing pregnant woman.
On Wednesday, Vivian Mitchell reported that she saw Laci Peterson walking her dog between 10 a.m. and 10:15 a.m. Dec. 24. She said she reported that to police but never received a return call.
Lee Peterson, Scott Peterson's father, reacted to that story Thursday.
"How do you follow up on a lead if you don't return someone's calls?" Peterson said by phone Thursday. "It makes me wonder about their competency. Here's an eyewitness account of my daughter-in-law and they don't follow up on it."
Police spokesman Doug Ridenour on Thursday confirmed that the department received the tip and said "it was appropriately handled during our investigation.
"But we have 8,000 tips," he said, "and the majority we haven't called back."
The Associated Press contributed to this report.