A Montana paleontologist whose past discoveries brought widespread acclaim intends to plead guilty to stealing dinosaur bones from federal land, in a case that highlights the illicit trade in rare fossils.

The change of plea motion from Nathan Murphy follows state and federal investigations into his alleged attempts to cash in on the highly lucrative fossil market.

Murphy, 51, is a self-taught dinosaur expert who spent much of the last two decades searching for bones in central Montana's Hell Creek formation — a rocky badlands once stalked by the fearsome tyrannosaurus rex.

He rose to fame in 2000 with his discovery of a mummified, 77-million-year-old duckbilled hadrosaur known as Leonardo, considered the world's best preserved dinosaur.

But after previously denying wrongdoing, court documents show Murphy has reached a plea deal on a federal charge that he stole bones from public land near Malta. He faced up to 10 years in prison if the case had gone to trial in early April.

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Murphy's case offers a rare glimpse into the illicit underside of paleontology, in which wealthy collectors are willing to pay hundreds of thousands of dollars for rare or unusual specimens.

While it's legal to take and sell bones from private property, federal law generally prevents their removal from public lands without a research permit. But the remoteness of many prime fossil grounds in Utah, Montana, Wyoming, Colorado and other western states makes enforcement difficult.

"There's probably somebody out stealing fossils from federal land in Montana today and we don't know about it because there's not enough law enforcement to patrol all of these sites," said Martin McAllister, a private archaeological investigator from Missoula.

Murphy's plea agreement comes 10 days after he pleaded guilty in state court to stealing a raptor fossil from private land and trying to cash in on molds from the specimen.

Casts made from those molds could have brought in from $150,000 to $400,000.

Earlier this week, Murphy told a reporter for The Associated Press that he's anxious to tell his side of the story on both the state and federal cases.

His attorney, Michael Moses of Billings, said Thursday that will have to wait until the federal plea agreement is accepted by U.S. District Judge Sam Haddon in Great Falls.

Murphy runs a paleo-outfitting business out of Billings that takes paying customers on weeklong dinosaur excavation expeditions. He was director of paleontology at the Dinosaur Field Station in Malta for 15 years before resigning in July 2007.

He left the museum shortly after the Montana Division of Criminal Investigation and the federal Bureau of Land Management began investigating his activities.

"He's devoted his life to that Malta museum," Moses said of his client. "We've entered into plea agreement with the U.S. Attorney's Office and we are going to make an appearance before the court to change our plea. At that point in time we'll be in a position to make a statement."