The first detective at the home of Laci Peterson the night she vanished told prosecutors that her husband's behavior made it difficult to eliminate him as a suspect.

In court Tuesday, Detective Allen Brocchini (search) testified he was summoned after several officers who had spoken briefly with Peterson deemed his story "suspicious."

Brocchini described Peterson that day, Christmas Eve 2002, as "calm, cool, relaxed" despite that his pregnant wife was nowhere to be found. He was set to be cross-examined Wednesday.

Also Tuesday, jurors heard a videotaped police interview of Scott Peterson that had been made Christmas Day. The interview had the tone of an interrogation, and climaxed with police testing his hands for gun powder residue.

Peterson, 31, is accused of murdering Laci in their Modesto home on or around Dec. 24, then dumping her body into San Francisco Bay (search). He says he went alone to the bay to fish; the government claims the fishing story is a cover-up.

Defense lawyers assert Laci was abducted and her captor framed Peterson after hearing his widely publicized alibi. They also say police focused too soon on Peterson, which caused them to miss other leads.

Laci Peterson's fetus, a boy the couple planned to name Conner, washed ashore April 13. Laci's body washed up from the bay a day later.

Brocchini said it was his job to rule out Peterson as a suspect — but testified that it wasn't easy.

At about 6:30 p.m. the day after his wife vanished, Peterson called Brocchini to check on the search.

"He wanted to know if we were using cadaver dogs. I told him we hadn't even considered Laci dead yet," Brocchini said.

On the video, Peterson gave often-muffled responses to Brocchini. The fertilizer salesman told the investigator that he fetched the boat from his warehouse in Modesto where he also e-mailed his boss, then drove to the bay.

After launching from a marina in Berkeley, he trolled around near an island about a mile from the dock and gave up after about 90 minutes without a catch. He then drove back, stopping for gas and dropping off the boat before returning to an empty home, he said.

Once back, according to the taped interview, he threw the jeans and T-shirt he was wearing into the washing machine, ate some pizza and jumped in the shower.

The fact that Peterson showered so soon after coming home "concerns me the most," Brocchini told Peterson. "That bothers me."

"What concerns me most is doing anything I can," Peterson replied, in an apparent reference to locating his wife.

After showering, Peterson called Laci's parents, who said they hadn't heard from her. A frantic search ensued.

Brocchini questioned Peterson about a pistol found in the glove compartment of his pickup truck and asked if he would submit to a "gunshot residue" test of his hands. Peterson complied.

Then came details of Peterson's affair with massage therapist Amber Frey (search).

Frey called the police department's tip hot line in late December and identified herself as Peterson's girlfriend, Brocchini said.

He said Peterson never mentioned anything about an affair.

Brocchini then went to visit Frey in Fresno where he bought her a telephone recording device to tape calls from Peterson.

"I said, 'Just keep talking to him and let him keep telling you whatever he's telling you,"' Brocchini said.

It is unclear exactly what is on the tapes, but Frey is set to be called as a prosecution witness. Defense attorneys may try to undermine her credibility after testimony from Laci's friends Monday that Frey spent numerous nights at their homes after the affair became public.

Peterson could face the death penalty if convicted.