The man in charge of collecting and preserving evidence at Robert William Pickton's farm testified at the murder trial Thursday that he was "overwhelmed" when he began the massive search.

Pickton is being tried in B.C. Supreme Court in New Westminster 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.

"It took two days to get over the feeling of being overwhelmed as I came to grips with just how large the scene was," Sgt. Tim Sleigh testified Thursday.

Sleigh provided the court with meticulous and graphic details of an almost two-year search of Pickton's four-hectare property in Port Coquitlam, including the initial discovery of the remains of two women.

Sleigh's testimony marked a difficult end to a week of graphic evidence for the jurors, who have now spent five weeks hearing the case against Pickton, the CBC's Natalie Clancy reported.

It was Sleigh's job to preserve evidence at the Pickton property. He told the court that bacteria is the most frequent destroyer of DNA evidence and the contents of more than one freezer on Pickton's farm spoiled before police were able to search them.

In April 2002, a strong odour coming from Pickton's garage forced police to search the building much sooner than they had planned, Sleigh said.

"I was very concerned that if we lost power to any of these freezers for a substantial amount of time, whatever was in these freezers would be spoiled," he said.

The crime scene expert said he entered Pickton's garage to see what was in a freezer covered with heavy tools and car parts and found human remains inside.

DNA analysis and dental record later confirmed those remains were those of Andrea Joesbury. Other remains found in a bucket underneath were later determined to be those of Sereena Abotsway.

Autopsy reminded expert of other unsolved case

These were the first human remains found on the property, but not the last.

Sleigh testified investigators later found partial remains of Brenda Wolfe, Mona Wilson, Georgina Papin and Marnie Frey not far from Pickton's trailer. The women — along with Joesbury and Abotsway — are the alleged victims in the current trial.

Pickton's defence team does not dispute that the six women's remains were found on the property, but maintains that Pickton didn't kill them.

Sleigh said he realized during the autopsy of Abotsway that he had seen similar remains in a 1995 unsolved murder case. In the 1995 case, police released a sketch of what the woman might have looked like, but never found out who she was.

Sleigh told the court that woman was the Jane Doe cited in a 27th first-degree murder charge against Pickton, which was dropped in 2006.

The Crown told the jury at the start of the trial that police found bones matching Jane Doe's DNA on Pickton's farm.

'It is graphic, it is harsh'

People who knew the women Pickton is accused of killing said that, as hard as it has been to hear all the evidence, they felt it was important for it to finally surface in court.

"It is graphic, it is harsh, it is horrible," Elaine Allen, who worked at Vancouver's WISH Drop-In Centre, told CBC News Thursday. Allen tried to help five of the six victims in the current trial.

"But having said that, we need to create awareness about what happened to the women who went missing from the streets of the Downtown Eastside, so we can prevent a tragedy like this from ever happening again.”

The court is on a break until Monday, when Sleigh will return to the stand. The trial is expected to last a year.