Police officers who dealt with Robert William Pickton in the 1980s considered him "mentally diminished," a crime scene investigator testified Tuesday at the B.C. man's trial in the deaths of six women.

Sgt. Timothy Sleigh told the B.C. Supreme Court in New Westminster that officers preparing to interview Pickton in February 2002 asked Sleigh for his assessment of the pig farmer based on his work on a previous investigation at Pickton's Port Coquitlam property.

"You described Willie as shy, hardly ever blinked and seemed mentally diminished," defence lawyer Adrian Brooks said.

Sleigh agreed he had.

Pickton's defence team has repeatedly asked witnesses throughout the trial about Pickton's mental capacity, the CBC's Natalie Clancy reported.

Pickton is being tried on six of 26 charges of first-degree murder in the deaths of missing women from Vancouver's Downtown Eastside, with a second trial to be held later. He pleaded not guilty to all charges.

Sleigh never revealed why the Picktons were the subject of an investigation by Port Coquitlam RCMP in the 1980s.

During a lengthy interrogation after Pickton was initially arrested, he spoke about an incident many years ago in which police investigated whether vehicles were dismantled and buried in his farm. But it is not clear whether Sleigh was involved in that investigation.

Sleigh also testified he told his colleagues that Pickton's younger brother, Dave, was "the brains of the two of them" and was condescending to his older brother.

Pickton didn't understand blood sample, says officer

In later testimony Tuesday, Staff Sgt. Ross Spenard testified that when he visited Pickton in jail to take a blood sample for DNA analysis, the accused did not seem to understand what he was doing.

"You explained the blood sample would be sent to a lab for DNA testing? You asked him if he understood, that he said no?" Brooks asked Spenard.

"Correct," replied Spenard.

Spenard also told the court that another man's fingerprint was found on an iced tea can in the same motorhome in which police found a blood-soaked mattress linked to Mona Wilson, one of the six women Pickton is on trial for killing.

The fingerprint was linked to a man named Gerald McLaughlin. The only other information the jury has heard about this man is that a receipt with his name on it was also found in the motorhome.

Another officer, Sgt. Fred Nix, testified Tuesday that on May 5, 2002, he was shovelling out a pig trough near Pickton’s slaughterhouse looking for evidence when he saw human remains.

"As I scrapped through material, this jumped out," Nix told the court.

DNA analysis and dental records later determined the remains were those of Brenda Wolfe, another of the women Pickton's accused of killing.

Nix was the 16th witness to testify at Pickton's trial, which is now in its sixth week. He also told the jury there were three dozen pig carcasses on the farm and that one animal was butchered the same way as some human remains found by police.

While the Crown continues to focus on evidence found on Pickton farm, the defense is directing the court's attention toward what police found at another property called Piggy's Palace, a social club where Pickton's brother held parties.