Amber Frey remembers recorded calls with Scott Peterson: 'I was shaking'

Frey opens up to "20/20" nearly 15 years after Peterson was sentenced to death.

— -- Amber Frey, the California woman who was romantically involved with Scott Peterson, talked to ABC about secretly working with police to help convict the now 44-year-old San Quentin prisoner of murdering his pregnant wife and unborn son.

Scott Peterson has served 12 years of his sentence after the remains of his wife, Laci Peterson, and their unborn son, Conner Peterson, were found a day apart in April 2003 on the shoreline of San Francisco Bay.

At nearly 8 months pregnant, Laci Peterson disappeared from her Modesto, California, home on Christmas Eve, 2002. According to reports, the 27-year-old was last seen by her husband Scott that morning.

Scott Peterson was convicted in November 2004 of first-degree murder for Laci's death and second-degree murder for the death of Conner.

Frey, then a 27-year-old a massage therapist and a single mother from Fresno, was a witness for the prosecution during Peterson's trial. From her testimony and her wiretapped phone conversations with Peterson, jurors learned that he had lied about being married in order to date Frey and continue a relationship with her.

In a recent interview with ABC's "20/20," Frey opened up about the case and the infamous telephone calls with her then-lover Peterson, which were recorded for Modesto police. Frey said she "had fear," but was willing to take risks to expose Peterson and help police in any way she could.

"[S]eeing this woman, knowing she's missing [and] she's pregnant," Frey told "20/20." "Being a mother ... at that point, it wasn't about me. It was about finding this woman."

Frey said that on Nov. 20, 2002, she met Peterson, then a 30-year-old fertilizer salesman, through a mutual friend. She said he told her he wasn't married.

"[H]e was good looking, he was nice, he was funny and attentive to me," Frey added. "All the things any woman would want."

The truth about Scott

Frey said it wasn't until a friend showed her a news article on a missing Modesto woman named Laci Peterson that she learned Scott Peterson was married. The article mentioned Peterson's truck and occupation, Frey said.

Convinced that the man described was her lover, Frey said she immediately called the Modesto Police Department hotline.

"I was in shock," Frey recalled. "I was crying, I have no idea how long. I was just trembling and I was like, 'It is him.'"

The following day, Frey said she reached Detective Albert Brocchini of the Modesto Police Department.

Brocchini and Detective John Buehler met with Frey in person and asked if she would be willing to tape conversations she had with Scott Peterson.

"As soon as we got it hooked up and discussed how it would work, he called," Frey said. "I was shaking tremendously. Sweating, just a mess ... trying to catch my breath, and [the police] were in disbelief like, 'I can't believe this guy just called her.'"

Lies and audiotapes

The recorded calls continued for nearly two months. During one phone conversation, which took place as loved ones gathered for a candlelight vigil in honor of Laci, Scott Peterson told Frey that he was celebrating New Year's Eve in Paris on a business trip.

Scott reveals Laci's disappearance

In another call that took place on Jan. 6, 2003, Scott Peterson reveals to Frey that he's been lying to her about traveling to Europe and about not being married.

Laci's family, who at first stuck by Scott Peterson during the initial phases of her disappearance, expressed shocked at the revelation.

Jan. 25, 2003: Scott and Frey speak one day after press conference

PETERSON: Ok, now I need to know from you, um, I am going to, um, speak to the press this coming week.
FREY: When?
PETERSON: During this coming week.
FREY: Do you have a date?
PETERSON: Um, well, I'm debating on when it should be done.
FREY: Okay.
PETERSON: Because Tuesday is, um, the State of the Union Address.
FREY: Okay.
PETERSON: So that will take up, you know, a lot of time.
FREY: I know it will.
PETERSON: And, um, and I want maximum coverage obviously. Uh, so it will probably be, um, with "Good Morning America."

Frey's phone conversations with Peterson continued at least until Feb. 19, 2003, and were played during Peterson's double murder trial, which began in summer 2004 in Redwood City, California.

She admitted to 20/20 that, after he was convicted, the thought that he could appeal was scary at first.

"If there's a point ... that they need me to testify again, or whatever else, then I'd be available to do so," she said. "But I don't spend my time worrying about things that aren't really real right now."