Mounties have singled out scores of taxi drivers in northern British Columbia for DNA samples as they investigate what happened to three sex-trade workers and a high school student who disappeared or were killed near the so-called Highway of Tears.

While the RCMP describe the work as routine, the Prince George Taxi manager who handed over the names of his 132 cabbies last fall says he wasn't expecting the scope to be so large or the requests to be so intrusive.

"I think they were treating it like a suspect list," Sam Kuuluvainen, who has managed the company for the past 10 years, said in an interview Tuesday. "I do believe this is connected in some way with the Highway of Tears."

Dozens of women have disappeared or been murdered along an 800-kilometre stretch of Highway 16 in northern British Columbia. Many were addicted to drugs or worked in the sex trade.

Advocacy groups have been calling for all of the women's cases to be looked at in their entirety. In 2005, police narrowed in on 18 cases they say share hallmarks and may be the work of a serial killer.

When police visited the taxi company, Kuuluvainen handed over his drivers' contact information because police told him two sex workers were murdered who were known to frequently ride cabs.

Then, to his surprise, he started receiving calls from his drivers, who told them they'd been asked to submit voluntary DNA samples. Kuuluvainen received a similar call.

"We focus on individuals that we believe had some form of contact with the (victim)," said Cpl. Annie Linteau of the RCMP.

Annie Linteau added that DNA samples are only used for the investigation they're gathered for, and then they're destroyed.

The RCMP continue to investigate the set of 18 similar cases along the highway between Prince Rupert and Prince George, under the umbrella of Project E-PANA. Linteau confirmed investigators approached one taxi company for help, but she wouldn't reveal the number of DNA samples they requested or whether there's been progress as a result.

She said the requests only relate to one person under Project E-PANA, 14-year-old Aielah Saric-Auger. The Prince George high school student vanished for two weeks before her body was found just off the highway in 2006.

The samples will also be applied to a woman who disappeared from Prince George in 2010, Natasha Montgomery, and two others who vanished from the city and were then found murdered, Cynthia Maas in 2010 and Jill Stuchenko in 2009. All three were known to work in the sex trade.

Reports from the Prince George Taxi drivers suggest RCMP called most, if not everyone, on his list, Kuuluvainen said. In many interviews, they were asked if they had information on the cases and if they had relations with prostitutes, he said. At the end of the interviews, they were asked to provide a sample.

"And if they didn't submit it, they would remain a suspect or a person of interest, that's what I was told from several drivers," he said.

Kuuluvainen said he didn't question providing the contact list because he'd been paid visits by police before, including in 2008, when they re-opened the investigation into Saric-Auger's death. Five or six of his drivers were questioned after police dug into the taxi company's call logs from the time the girl disappeared, he said.

This time, at least two of his drivers refused, he said -- a middle-aged woman and a man who's worked for the company for three decades.

"With this DNA thing, as far as I know it's cleared everybody, but the other side of it is where does it stop? How far does the RCMP go with a theory?"

Linteau said she can't speak to the investigators' methods, but stressed no one is forced to provide a sample. She said about 600 samples have been collected in connection with Project E-PANA during the past six years.

"We're hopeful that this will help narrow the focus of our investigation by ruling out the involvement of certain individuals," she said. "At the end of the day, what we want is to provide closure to the families."

When police asked Kuuluvainen for an interview, two months or so after the requests started, he explained he owned a cab but hadn't been driving for more than a year. The officers thanked him and left it at that.

"We're still going to co-operate with the RCMP, but the next time they are asking for information I think I may be asking a few more questions," Kuuluvainen said. "If I don't like the answer, I may be asking for a warrant next time." He noted a Prince George bylaw requires all cab drivers to get a criminal record check every year.