Scott Peterson (search) lowered his head and shed a tear when told the remains of his missing wife, Laci, and the fetus she carried had been found along San Francisco Bay, a detective testified Thursday.

Detective Craig Grogan (search), who led the investigation for the Modesto Police Department, recounted for jurors the events that led to Peterson's arrest on April 18, 2003, the same day the bodies were identified through DNA testing.

Grogan said the decision was made to arrest Peterson before the test results were known because media coverage of the case was intensifying and he feared Peterson might try to flee once news of the identities got out.

Peterson was found at a San Diego golf course.

"I told him that he was under arrest for murder," Grogan said, noting Peterson wasn't wearing his wedding ring.

The arrest came shortly before Grogan received a call saying the bodies were those of Laci and the fetus. The detective relayed the test results to Peterson immediately.

"He and I were seated beside each other in the back of the car. ... I gave him that information. ... He removed his sunglasses. I saw that he had lowered his head, a tear came out of his right eye, then he wiped the left side of his face," Grogan said.

Earlier, Grogan testified that police followed several leads before arresting Peterson, including the possibility of a serial killer.

Grogan said Peterson's mistress, Amber Frey (search), and even Laci's family members had been considered suspects. Prosecutors allege it was Peterson's affair with Frey that drove him to kill his wife.

Defense lawyers have accused police of focusing too quickly on Peterson to the detriment of other possible leads.

Prosecutors allege Peterson killed his Laci, who was eight months pregnant, on or around Dec. 24, 2002, in their Modesto home, then dumped her weighted body into the bay. Her remains — and that of the fetus — washed up in April 2003, not far from where Peterson launched his boat on Christmas Eve for what he claims was a solo fishing trip.

Peterson's lawyer, Mark Geragos, maintains someone else abducted and killed Laci.

On cross-examination, Geragos pointed out that Peterson was cooperative and truthful with police on the first night of the investigation.

Geragos then sought to show that police honed in too quickly on his client, noting one officer told a witness on that first night that he "already knew what happened."

Police have testified previously that a roll of chicken wire found in Peterson's truck made them suspicious, although it has never been linked to the crime.

Geragos noted that Peterson told the officers it was to be used to fence off some trees in his back yard because the couple's cat had been scratching the bark.

Grogan confirmed that not only were there scratch marks on some trees, but he saw a cat clawing a tree during one search of the Petersons' home.

Later Thursday, Geragos provided an explanation for why Peterson visited the Bay Area several times while police were searching for the bodies there: He was looking for a witness who had seen him put his boat in the water Christmas Eve. Geragos said Peterson had even hired a private investigator to help find the person.

The defense lawyer also tried to counter prosecution claims that Peterson lied to some people about his alibi. Geragos said Peterson left his wife a telephone message hours before he arrived home, telling her he was just leaving the bay marina — a point intended to show Peterson never meant to conceal anything about where he had been that day.