Scott Peterson's (search) murder trial resumed Thursday with more testimony about police surveillance of Peterson in the weeks after his pregnant wife vanished.

Mark Weiglein, an officer with the Modesto Police Department assigned to follow Peterson, testified under cross-examination that Peterson spent more than five hours on the morning of Jan. 4 at the volunteer center set up to help find his wife, Laci, and later spent time posting numerous fliers.

During testimony Wednesday, prosecutors implied Peterson was so worried his wife's body would surface in San Francisco Bay that he visited the area several times after reporting her disappearance, but defense lawyers say he was simply checking on the search efforts.

Thursday, Weiglein said that around 4:30 p.m. Jan. 4, authorities watched as Peterson and friends searched a construction yard in the town of Manteca, about 17 miles north of the Petersons' hometown of Modesto.

"And they were all three looking around picking up material?" defense lawyer Mark Geragos (search) asked.

"That is correct," Weiglein said, adding that officers did not know what the group was doing.

"Did anybody that you're aware of ever go and see ... that location to see if that had anything to do with a tip that came in that that's where Laci Peterson (search) might be?" Geragos asked.

Weiglein was unaware of the tip.

Defense lawyers have suggested that Peterson was actively searching for his wife in the weeks after he reported her missing on Dec. 24, 2002.

Prosecutors called numerous police witnesses Wednesday who tailed Peterson in the weeks after his pregnant wife disappeared.

Prosecutors allege Peterson killed his wife in their Modesto home on or around that Christmas Eve, then drove to San Francisco Bay, launched his boat from the Berkeley Marina and dumped her body. The badly decomposed remains of Laci Peterson and the couple's fetus washed ashore in April 2003, not far from where Peterson set out for what he claims was a solo fishing trip the day Laci vanished.

Defense lawyers contend someone else abducted and killed Laci, then framed their client after learning his widely publicized alibi.

On Wednesday, witnesses described how Peterson visited the Berkley Marina three times -- on Jan. 5, Jan. 6 and Jan. 9 -- as police scoured the bay for Laci's body. Prosecutors and witnesses noted that Peterson even drove rental cars at times and appeared to attempt to elude authorities.

On cross-examination of prosecution witness Jeff Mackanin, a state Department of Justice investigator assigned to follow Peterson at times, Geragos noted that Peterson also visited a reservoir miles away from the marina after learning from a newspaper article that police were considering a search for Laci there.

Mackanin said he had no knowledge of that. Geragos was implying Peterson was simply going everywhere police were searching for his wife's body in hopes of finding some clues.

Police testified they followed Peterson's movements from Jan. 3-11, 2003.

Alexander Bettis, an undercover officer with the Modesto Police Department, testified Peterson visited the marina on Jan. 5 and Jan 6, first in his own car, then in a rented red Honda Civic.

Bettis also said that each morning Peterson would go to the volunteer center set up to help search for Laci and was often seen putting up missing fliers with her picture.

"I was trying to maintain surveillance. It was kind of a cat-and-mouse type thing," Bettis said, adding that at one point it appeared that Peterson knew he was being followed.

On cross-examination, Geragos highlighted the fact that Peterson began every day at the volunteer center and spent much time putting up fliers in search of his wife.

The trial resumed Wednesday morning with the cross-examination of Eloise Anderson, a search dog handler with the Contra Costa County Search and Rescue team, who testified her canine picked up Laci's scent on Dec. 28, 2002, at a Berkeley Marina pylon at the water's edge.

Geragos has attempted to show the scent-sniffing techniques are based on theory, not science, noting that Trimble failed a test two months earlier that was similar to the tracking technique used to pick up Laci's scent.

The defense lawyer played for jurors a video of the training exercise where Trimble was seen trying to track a subject in a vehicle. The dog wandered in and out of bushes along the road, sniffing the sidewalk and turning in the opposite direction before stopping and barking at the person videotaping the exercise.

"The dog just alerted on the videographer, right?" Geragos asked.

"No. She barked at me," Anderson said.

The dog again circled back in the opposite direction and the test was stopped. Anderson acknowledged the dog failed the test.

However, prosecutors noted on redirect that the dog eventually picked up the search subject's scent later at the command center where the exercise began.

Geragos also noted that Anderson left the so-called failed exercise out of her report and that the tape only surfaced last month.

Geragos implied that only after he issued a subpoena to Contra Costa County authorities on Aug. 3 did the tape surface. Geragos said he received an e-mail the next day from prosecutors acknowledging the tape's existence.

Anderson insisted she hid nothing and said she didn't know the Trimble test was on the tape until early this year, when she said she turned it over to Contra Costa County authorities.