Federal prosecutors are seeking a major sentencing break for an activist who committed arson at Michigan State University, publicly acknowledging for the first time his wide-ranging undercover role in investigations of eco-terrorism.

Frank Ambrose of Detroit recorded 178 conversations with other targets, putting himself at risk as he traveled out of state to help the FBI, the government said.

His cooperation "has been nothing short of remarkable, both in terms of the time and effort he put into it and in terms of its value to federal law enforcement," Assistant U.S. Attorney Hagen Frank said in a court filing Friday.

Frank is asking a federal judge in western Michigan to cut Ambrose's sentencing range to roughly eight to 10 years in prison, well below the 20-year maximum. A hearing is set for Oct. 20.

An explosion and fire caused more than $1 million in damage at MSU's Agriculture Hall on New Year's Eve 1999. It was a protest against genetically modified crops in the name of a radical group, the Earth Liberation Front, or ELF.

In March, more than eight years later, Ambrose pleaded guilty to conspiring to set that arson, as well as another fire that damaged logging equipment in northern Michigan.

He also took responsibility for many other acts committed from 1999 to 2003, including six arsons of boats and new home sites in Michigan and Indiana. The property he destroyed was valued at more than $2.5 million.

Ambrose, 33, became an informant in 2007, a few months after making a critical mistake: He dumped personal records, writings, a gas mask, an M-80 explosive and other possessions in a Detroit-area trash bin. A man foraging for scrap cardboard called police, and the FBI subsequently raided Ambrose's home.

He turned on a co-defendant, ex-wife Marie Mason, who has pleaded guilty to the MSU arson, but his cooperation with the government goes beyond Michigan. Continued...