The investigation into two 2006 spills that allowed thousands of gallons of oil to soak the tundra wasn’t played out when the U.S. Department of Justice called it quits, according to a complaint filed this month by an nationwide environmental group.

Public Employees For Environmental Responsibility requested a probe into the shutdown, implying the Department of Justice could have been politically motivated to end a felony investigation of British Petroleum’s role in leaking more than 250,000 gallons of oil from the Prudhoe Bay oil field. The spill is considered to be the largest in Alaska’s North Slope area.

In 2007, the department allowed the oil company to plead guilty to one misdemeanor charge and pay $20 million in penalties, according to the group’s press release. It did so over the objections of Environmental Protection Agency (EPA) Special-Agent-In-Charge Scott West, who asked for an extension of the 18-month investigation.

“Never … have I had a significant environmental criminal case shut down by the political arm of the Department of Justice, nor have I had a case declined by the Department of Justice before I had been fully able to investigate the case,” West stated in the release. “This is unprecedented in my experience.”

West, who recently resigned his post, believed a Bush appointee to the Justice Department’s Environment and Natural Resources Division ordered the shutdown.

Allegations “that something sinister took place” are “simply not true,” according to a Department of Justice statement quoted in a McClatchy news article. “As with any investigation, there comes a point in time when further investigation is no longer warranted if it does not have a realistic chance of generating useful evidence.”

The probe request is under review by the Department of Justice Inspector General’s office.