Officials spoke to the AP on the condition of anonymity because they were not authorized to discuss the case.
Norton could not be reached immediately for comment.
"We are aware of an investigation; however, we are not in a position to comment," said Kelly op de Weegh, a Shell spokeswoman.
The Interior Department's Office of Inspector General began the investigation toward the end of Bush's last term, after receiving complaints about the lease process. The IG's office made a formal referral to the Justice Department earlier this year after concluding there was probable cause of a criminal violation.The investigation was first reported by The Los Angeles Times. Prior to becoming Bush's first Interior secretary, Norton was Colorado's attorney general and had worked as a private lawyer for timber, oil and mining companies. At Interior, she supported expanded oil and gas drilling on government-owned land. The development of oil shale largely in the West was one of the technologies that the Bush administration wanted to explore aggressively. In response to a recommendation by then-Vice President Dick Cheney's energy task force, the Interior's Bureau of Land Management issued six demonstration leases in Colorado and Utah.