A Modesto woman said she saw a tarp covering a large object in a fishing boat Scott Peterson pulled with his pickup early Christmas Eve 2002.

Authorities discounted the account because it did not jibe with the way they intend to prove how the fertilizer salesman disposed of his pregnant wife's body, the possible witness said.

And Peterson's defense team has no interest in an account that could hurt his alibi.

The unwanted witness, at times shaking, said she hoped to unload an emotional burden after making certain she will not testify at Peterson's trial. But she asked to remain unidentified for fear aggressive reporters would make her life miserable.

One source close to the investigation said the woman was interviewed but was not subpoenaed to testify at the trial.

"Not one day goes by that I don't think about this," the 43-year-old woman said.

Her 25-year-old son said she told him and his sister about a suspicious man the day she saw the pickup and boat. They did not realize the significance, mother and son said, until a couple of days after news crews descended on Modesto.

Peterson, 31, could face the death penalty if convicted of murdering his wife, Laci, and their unborn son, Conner. Jury selection is under way in Redwood City, where the trial was moved because of crushing publicity.

The potential witness said she approached an intersection in the Petersons' La Loma neighborhood between 7 and 7:30 a.m. that Christmas Eve. About the same time, a pickup pulling a boat trailer approached on the street to her right, she said. She put on her left blinker and waited because the truck had stopped first, she said.

But the driver, who appeared headed in the same direction, refused to proceed. She said the man appeared ill at ease and became increasingly agitated.

Their eyes met briefly, and he quickly turned right instead, she said. The right rear trailer tire went over a curb, she said.

"When the news was coming out and there was more and more media, the more scared I became," she said.

Witness passed around

She did not immediately go to police because she figured others must have seen the boat and because she was confused when some people said they saw Laci Peterson alive later Christmas Eve morning.

The woman said she eventually tried to call detectives, who were inundated with thousands of leads, but their voice mail-boxes were full. A few weeks later, she unloaded her story on a police officer while in the parking lot of a fast food restaurant, she said.

Because she lives outside the city limit, she said, the officer sent her to the Stanislaus

County Sheriff's Department. Deputies explained that the case belonged to Modesto police.

Police then referred her to the district attorney's office, she said. In April 2003, an investigator took notes as they re-created her encounter where Miller Avenue meets La Loma and Santa Cruz avenues.

In August, a prosecutor told her that her testimony was not needed because it conflicts with Scott Peterson's cell phone records, she said.

The records indicate that he began a call near his Covena Avenue home at 10:08 a.m. Dec. 24, 2002, an investigator testified at Peterson's preliminary hearing in November. That would have been about three hours after the woman said she saw Peterson, his truck and his boat.

No witnesses at the hearing said they spotted the boat at Peterson's home.

And, prosecutors at that time intended to introduce evidence from tracking dogs suggesting that Laci Peterson -- or her body -- traveled south on Santa Barbara Avenue. That route is one street west of Santa Cruz Avenue, where the woman said she saw Scott Peterson.

A judge refused to allow that dog-tracking testimony, calling it "iffy" and "inconclusive."

Authorities, subjected to a gag order, have closely guarded their evidence. But they assured the woman they have "eyewitnesses out in the Bay Area where he was fishing," she said.

"They said, 'Don't worry; if it makes you feel better, we have a good case,'" she said.

It was not clear why authorities think her account conflicts with their theory. She noted that Peterson could have turned onto Santa Barbara, where the dogs picked up his wife's scent. And he might have unhitched the boat at his Modesto warehouse before returning home that morning.

At the preliminary hearing, Steve Jacobson, an investigator with the district attorney's office, used Peterson's cell phone records to place him at or near his home at 10:08 a.m. and moving toward his warehouse. But Jacobson's answer did not rule out calls placed earlier, or the possibility that Peterson left home earlier.

At the hearing, prosecutor Rick Distaso asked Jacobson, "Do you know when the first call was made?"

Jacobson answered: "The first call that you had me look into was at 10:08 a.m."

Peterson told police he left his home about 9:30 a.m. Dec. 24 to fish alone in San Francisco Bay, another detective testified. The defendant said his wife was mopping a floor when he left and planned to walk their dog; the defense theory is that someone kidnapped her.

Authorities with tunnel vision?

Peterson's attorneys have criticized investigators for having tunnel vision that kept them from seriously pursuing leads that could have led to the "real killer."

"Your (investigative) instincts and experience take you far," said Miami attorney Jayne Weintraub, who has defended such high-profile clients as Rosie O'Donnell and former baseball star Jose Canseco. She prosecuted murder cases for eight years before becoming a defense lawyer in the 1980s.

"The bad part is, you miss stuff" by discounting some clues, Weintraub said. "Police make mistakes all the time. They're not infallible. People need to realize that."

High-interest cases often attract people who crave attention and might try to insert themselves into the action, said Ruth Jones, a former New York City prosecutor now teaching at Sacramento's McGeorge School of Law.

That this potential witness is going out of her way to avoid the spotlight helps her credibility, Jones said. But she noted that it is impossible to assess why authorities discount her story, as long as the gag order keeps evidence under wraps.

The woman said she is ashamed that she did not come forward sooner.

"I want to apologize to Laci's mom, to her family," the woman said, crying. "I'm very shy and sensitive, and I was worried about my family. I should have been more concerned about her family. How could I call and say, 'I think your daughter may be dead?'"

She said she told police she would take a lie-detector test, and her children would do the same regarding their conversation before the story broke about the missing woman. She noted that police hypnotized two other potential witnesses in an effort to help their memories.

"Police are willing to put people under hypnosis for what they think they saw, while I know what I saw," she said.

"I wish to God I had gone to police that morning," she continued. "I'm tormented by this. But as God is my witness, I know what I saw that morning."

Bee staff writer Garth Stapley can be reached at 578-2390 or gstapley@modbee.com.