Modesto Police Detective Craig Grogan, the lead investigator, recounted for jurors the events that led to Peterson's April 18, 2003, arrest in San Diego.
The same day, DNA testing was being conducted that would later identify the bodies. Media coverage was intense, Grogan said, later implying that he feared Peterson might try to flee once the bodies were positively identified.
Grogan said he "didn't want Mr. Peterson to be able to get away."
Eventually, the decision was made to arrest Peterson before the identifications were determined, Grogan said. Peterson was stopped by authorities at a San Diego golf course.
"I told him that he was under arrest for murder," Grogan said, noting that Peterson wasn't wearing his wedding ring.
Once Grogan got the call that the bodies were indeed those of Laci and the fetus, he gave the news to Peterson.
"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.
Also Thursday, jurors in the Scott Peterson trial saw
Earlier, Grogan testified that police followed a number of leads in the case before arresting Peterson, and even looked into the possibility of a serial killer.
Grogan said many suspects were considered, including Laci's family members and Peterson's mistress, Amber Frey. Prosecutors allege it was Peterson's affair with Frey that drove him to kill his wife.
One tip Grogan said he ruled out came from a man who confessed on a hot line to the killing. The man was "located in a mental hospital on the East Coast," Grogan said.
Defense lawyers have accused police of focusing too quickly on Peterson to the detriment of other possible leads.
Prosecutors allege Peterson killed his eight-months-pregnant wife 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.
Defense lawyers maintain someone else abducted and killed Laci.
On cross-examination, defense lawyer Mark Geragos noted 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 that 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.
Geragos also tried to counter the prosecution theory that Peterson made cement anchors to sink his wife's body in the bay.
Peterson told police he made one anchor for his boat and used the rest of the cement for work around his house, including filling in holes in his driveway. Prosecutors claim he made five anchors, only one of which was recovered from the boat. They claim the rest were tied to Laci.
Previous witnesses have testified that the cement from Peterson's anchor and cement taken from his driveway didn't match, a contention the defense has tried to rebut.