Former Interior Secretary Gale Norton didn't use her power to grant lucrative shale leases to Royal Dutch Shell PLC, which hired her less than a year after she left office in 2006, according to the Interior Department's inspector general.

In a report issued late last week, the IG found that Norton -- who served as George W. Bush's Interior chief from 2001 to 2006 -- was closely involved in the Bureau of Land Management's research and development leasing program for oil shale on public lands, with a former colleague describing her as "pushing oil shale big time."

But while BLM appeared to give Shell preferential treatment over other companies by issuing the company three leases of up to 15,000 acres, Norton did not violate any ethics laws, the investigation found.

"We found that Norton was very interested in the [research, development and demonstration] program during her tenure as secretary," acting Inspector General Mary Kendall wrote. "But we did not find evidence to conclusively determine that Norton violated conflict-of-interest laws, either pre- or post-employment with Shell."

The Justice Department, upon reading the IG's findings, declined to pursue a criminal case, the report says.

The 23-page report found that Shell likely received inside information from someone at BLM in order to submit its first of three lease applications the same day Interior posted the solicitation in the Federal Register.

Other companies -- which had been told they could only submit one application -- did not apply until 82 days later, the report says. An Interior employee also made corrections to acreage on two of Shell's applications so that the proposals would not have to be rejected by BLM, according to the report.

Norton, along with several other Interior officials, began working for Shell after the oil shale RD&D leases were issued, according to the report.

A Utah entrepreneur cited in the report said it was not a coincidence that Norton went to work for Shell after overseeing the process through which the company was awarded three of the six oil shale leases.

"We determined that some of the entrepreneur's allegations were correct, and that BLM actions at least appeared to give Shell preferential treatment," the report says.

Norton was also found to have attended or been briefed on 12 meetings on oil shale in 2005 and 2006, including some with top-ranking Shell officials in attendance, according to the report.

Kit Kimball, former director of Interior's Office of External and Intergovernmental Affairs, told IG investigators that Norton and her staff "didn't totally trust the BLM," and that Norton knew Shell was ready to proceed with its oil shale development program and felt she needed to be involved to make sure BLM's program got it right.

"She knew Shell wanted to get going," Kimball said, according to the report.

Norton this weekend lashed out at the IG for wasting millions of taxpayer dollars in a futile search for wrongdoing.

"The Interior inspector general's office wasted millions of taxpayer dollars in an attempt to find imagined wrongdoing," Norton said in an e-mailed statement quoted by The Wall Street Journal.

Norton said that she was unemployed for nine months after leaving Interior and had interviewed for "a number of different positions" before joining Shell, according to the Journal.

In a statement, House Natural Resources Chairman Nick Rahall (D-W.Va.) said, "It sounds like Secretary Norton was earning her salary from Shell even before they put her on the payroll."

David Abelson, of Western Resource Advocates, an environmental group that has opposed new oil shale leasing on public lands, said he was surprised Justice had decided not to charge Norton for wrongdoing but that he trusted it was the right decision.

Still, "As the IG makes clear, Secretary Norton was more concerned about private gain than protecting the public interest," he said. "Shell's actions from this point forward must be carefully scrutinized."