Prosecutors in the case against accused double murderer Scott Peterson (search) decided not to introduce wiretap evidence at the preliminary hearing, which opened Wednesday.

The development sparked speculation over whether the much-publicized taped phone conversations between Peterson and his extramarital girlfriend Amber Frey would be played in court if he is forced to stand trial.

Prosecutors began presenting evidence Wednesday that Peterson murdered his pregnant wife, Laci, and their unborn son 10 months ago.

The first testimony revolved around the issue of mitochondrial DNA — specifically whether a strand of hair found in a pair of pliers on Peterson's boat was admissible evidence. The prosecution said yes, the defense said no.

For much of an hour FBI lab supervisor Constance L. Fisher explained the method of molecular biology used to analyze the hair found in the boat Peterson said he used to go fishing on the day his wife disappeared.

But Peterson's defense lawyer Mark Geragos disputed the admissibility of the mitochondrial DNA evidence in the case, and also suggested that someone may have tampered with the hair found on the boat. It was originally listed as a single hair, but prosecutors said it broke in half during their investigation.

The hearing, which began about 12:30 p.m. EST, will ultimately determine whether the case will go to trial. Peterson could face the death penalty if he's found guilty.

The hearing was expected to reveal the most details to date of the evidence amassed by investigators in the case that riveted the nation after 27-year-old Laci, a substitute teacher, disappeared on Christmas Eve.

• Raw Data: Criminal Complaint, People v. Peterson (pdf)

The families of Scott and Laci Peterson were brought into court separately on Wednesday, and didn't speak to each other or make eye contact.

Stanislaus County prosecutors said they would call the couple's housekeeper or one of Laci Peterson's family members as the next witness. But the DNA testimony was expected to take much of a day that began with 20 minutes of outlining ground rules and procedural matters.

During that session, Stanislaus County Superior Court Judge Al Girolami granted Geragos a gag order against Gloria Allred, attorney for Frey — who is one of the the prosecution's key witnesses. Geragos pointed out that other witnesses have been excluded from the courtroom and said he didn't want Allred to tell Frey the testimony of other defense witnesses.

Scott Peterson reported his wife missing when he returned home the night of Dec. 24 from a solo fishing trip near Berkeley. His wife was eight months pregnant with a boy they planned to name Conner.

The case was portrayed as an American tragedy, with Laci's smile beaming from photos and videos. The expectant parents seemed like the all-American couple until Scott Peterson's mistress surfaced and he admitted having an extramarital affair.

After Peterson and other family members led hundreds of volunteers to search canals, reservoirs and wildlands, the decomposed remains of the mother-to-be and her fetus were found nearly four months later in April by dog walkers, within miles of where Peterson said he had been fishing Dec. 24.

The arrest and subsequent hearings did little to unveil what clues led investigators to suspect her husband from the beginning.

Leaks led Judge Al Girolami to impose a gag on participants in the case and seal most of the police records to protect Peterson's right to a fair trial.

Voluminous court filings have provided glimpses of the evidence defense lawyers will try to prevent prosecutors from presenting: DNA analysis of Laci Peterson's hair found on pliers in Scott Peterson's boat, bloodhounds used to pick up the scent of Laci Peterson in the boat or at a storage warehouse her husband rented, and wiretaps and global positioning systems used to monitor and track Scott Peterson.

The 31-year-old former fertilizer salesman has been held without bail since he was arrested in San Diego County — not far from the Mexico border — with his hair bleached and $10,000 cash.

Defense attorney Mark Geragos has said he would not only prove Peterson innocent, but would find the "real killers." The defense team has intimated that a satanic cult may have been responsible. Police have disputed such claims.

Prosecutors are expected to present enough evidence so the charges stick, but not so much that they expose witnesses to tough cross-examination.

"You may get an unusual case where the prosecution thinks if it comes on like gangbusters the defendant will switch their plea to guilty," said Evan Lee, a professor at the University of California Hastings College of the Law. "I have a funny feeling that's not going to happen in this case."

Nearly 200 applications for the fewer than two dozen sets of courtroom credentials were received from reporters, including a TV news crew from Japan. News trucks were in place outside the courthouse at the beginning of the week, and more than 100 phone lines have been installed.

"We're putting on a mini Super Bowl is what we're doing," said Kelly Huston, spokesman for the Stanislaus County sheriff. "It swamps everything by far. This is the event that trumps all other events locally."

Fox News' Claudia Cowan, Greta Van Susteren, Catherine Donaldson-Evans and The Associated Press contributed to this report.