As many as 30 people have responded to a police request to supply DNA samples to assist an investigation into the fate of 50 missing B.C. women, which is now focused on a trailer on a suburban pig farm.

On Wednesday, police said they had found "specific items of interest" within the trailer containing DNA and urged people who might have visited the mobile home on the Port Coquitlam farm to come forward.

RCMP spokeswoman Const. Cate Galliford said the DNA testing would help eliminate people from the investigation and add to their information and urged more people to come forward.

"By giving us DNA samples, investigators ... will be able to further narrow down the identity of the DNA samples found inside the trailer," said Galliford.

BC-CTV reports that one of the owners of the farm, Dave Pickton, told police that his brother, Robert William, slept in the trailer. He also said the trailer was used as an office for a topsoil business and as many as 4,000 people have gone in and out of the mobile home, mainly his employees.

As many as 40 investigators have been combing the Port Coquitlam farm, located about 30 kilometres east of Vancouver, since Feb. 5. The farm was notorious among residents of Vancouver's downtown eastside for its frequent parties often involving alcohol and drugs.

Police are keeping details of the investigation largely under wraps.

"There have been questions about why a refrigeration truck was brought on site by police and what is being loaded into that truck," said Vancouver Det. Scott Driemel. "We are not going to answer any questions about that action."

Most of the women who disappeared between 1983 and late 2001 worked as prostitutes in the seedy downtown eastside.

While police continue their investigation of the farm in a search for clues, hundreds of people marched through the downtown eastside in what has become an annual Valentine's Day commemoration for the missing women.

The raid of the pig farm began after Robert Pickton was arrested on a weapons charge. He was later released. After the first raid, police obtained a second court order to search the farm as part of the missing women investigation.

Police won't say what evidence prompted the second search, but local news reports have named personal items, such as an inhaler, as some of the personal belongings found on the farm. Police have not named the Pickton brothers as suspects in the disappearances.

In an interview published Thursday in the Vancouver Province, Dave Pickton said his brother is "suffering" from the investigation.

Pickton also discussed an alleged stabbing on the farm in 1997 that led to Robert being charged with attempted murder and forcible confinement. The charges were later stayed.

After the charges were stayed, he said Robert began buying impounded cars from police. In one case, Dave Pickton said the interior of a van bought from a police impound lot was so smeared in blood it made him sick.

Some of the other vehicles they bought were loaded with garbage and discarded women's clothing, he said.