The BC SPCA is preparing for the grisly task of exhuming the remains of roughly 100 sled dogs killed last year and buried in a mass grave near Whistler, B.C.

The association says it had to wait until the frozen ground thawed before unearthing the remains of the animals, allegedly killed in April 2010. Excavation is expected to begin on May 5 and last three to four days.

SPCA members will be joined by a team of forensic experts from across North America, some of whom aided in the investigation of serial killer Robert Pickton.

"This is one of the largest and most complex investigations the BC SPCA has ever undertaken," the agency's general manager of cruelty investigations, Marcie Moriarty, said in a release.

"Because of the length of time that has passed since the incident occurred, it is necessary to employ painstaking, state-of-the-art forensic techniques to gather the evidence needed to pursue animal cruelty charges in this case."

The SPCA estimates the investigation could cost up to $225,000.

News of the cull surfaced in January after workers' compensation documents were leaked to the media. The documents outlined a claim by a worker who said he was experiencing post-traumatic stress after killing the dogs.

The animals were under the control of a Howling Dog Tours. Another firm called Outdoor Adventures had a stake in the company when the cull took place, but insists it had no idea about the cull.

The worker alleged the dogs were shot or had their throats cut over the course of two days.

Following the public outcry, the B.C. government appointed a task force to review the local dogsled industry. The task force published 10 recommendations last month, which include boosting penalties for animal cruelty, instituting standards for the sled-dog industry and increasing funding for B.C.'s SPCA.

Premier Christy Clark endorsed the report's recommendations after it was released and pledged to enact what she called the toughest animal cruelty legislation in the country.

With files from