Investigators in Laci Peterson's (search) disappearance once considered the pregnant schoolteacher might have been poisoned by her husband and that's why police were unable to find a bloody crime scene, according to testimony Tuesday.

"One of the theories at some point was maybe Laci Peterson had been drugged, is that right?" asked defense lawyer Mark Geragos (search).

"Yes, we looked into that," said Modesto police Detective Craig Grogan (search), who has been on the witness stand for more than a week.

Grogan, the lead detective assigned to the case, said police considered the poison theory because they were unable to find any signs of a struggle and found none of Laci Peterson's blood in the couple's Modesto home, where prosecutors allege the murder took place on or around Dec. 24, 2002.

Grogan said that during a Feb. 18, 2003, search of the Petersons' home, police seized, among other things, a mortar and pestle to have them examined for the existence of any drugs. None were found, he said.

Meanwhile, Judge Alfred A. Delucchi (search) told jurors Monday morning the prosecution would not wrap up its case this week as previously intended.

"Hopefully we'll finish the prosecution case by next week; we'll see," Delucchi told jurors.

The trial is now in its 18th week.

On Monday, Peterson's lawyers suggested his wife's abduction and murder may have been the result of mistaken identity by perpetrators seeking to attack a virtual look-a-like.

Geragos noted during questioning of Grogan that authorities had received a tip early on from a woman whom the lawyer only identified as "Michelle" about the possibility that Laci's killing may have been a mistake.

The woman worked as a prosecutor in Merced County and lived near the Petersons' home in Modesto, Geragos said.

He described her as looking very similar to Laci Peterson and noted the woman had given birth to a child in October 2002. The woman walked her dog — oddly, the same kind the Petersons had with the same name, McKenzie — in the Petersons' neighborhood.

The woman had recently been threatened after prosecuting a case.

She called police after Laci vanished to report that the alleged abductors "might have mistaken Laci Peterson for her, correct?" Geragos asked the detective.

"Correct," Grogan replied.

It was just one instance Monday where the defense attorney used Grogan to attempt to create reasonable doubt that his client is the killer.

He noted that police did not take seriously many of the reported sightings of Laci on the day she was reported missing — Dec. 24, 2002.

Geragos highlighted one tip specifically where a man claimed to have seen Laci that morning. The tip came within a week of her disappearance.

"Is it a fair statement that nobody contacted him ... until approximately six weeks ago during this trial?" Geragos asked.

"That's correct," Grogan replied. "I can't say that the sightings were automatically a priority for us at that time."

Grogan also backed up another key defense theory that the pregnant schoolteacher had planned to walk the couple's dog the morning she vanished.

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

Defense lawyers maintain someone else abducted and killed Laci while she walked the couple's dog in a nearby park. The dog was found by a neighbor in the street the morning Laci vanished, according to previous testimony.

Prosecutors claim Laci had stopped walking the dog weeks earlier at her doctor's request, and that Peterson set the dog loose to make it appear as if someone else abducted her.

But Grogan acknowledged Monday that Peterson told police on the first night of the investigation that Laci had planned to walk the dog that morning. Sharon Rocha (search), Laci's mother, told Grogan a few days later that Laci walked the dog every morning, the detective testified.

Geragos then suggested that Laci knew about her husband's affair with massage therapist Amber Frey. The defense lawyer later surprisingly brought up two previous affairs.

Grogan testified that a relative of Scott Peterson's told him that Peterson had told her Laci knew about the affair with Frey and, according to the police report, she was extremely angry.

Grogan acknowledged the woman told him that "Laci insisted that they not tell the parents about it," Geragos quoted from the report.

Geragos later had Grogan detail two tips from women who claimed to have had affairs with Peterson while he and Laci lived in San Luis Obispo in the 1990s.

The defense lawyer noted that one of Laci's friends told Grogan that Laci had told her about a week before she vanished that she was "not having sex anymore ... it was not a priority."

It appeared as if Geragos was offering an excuse for Peterson's repeated philandering, while also noting that he never killed before. Prosecutors allege Peterson's affair with Frey was his motive for murder.