IOWA CITY, Iowa - A Minneapolis man has pleaded guilty to bumping a federal prosecutor in Iowa two years ago after his son was sentenced and immediately imprisoned for his role in a 2006 attack on a ferret farm attributed to the Animal Liberation Front.

Timothy DeMuth, 51, pleaded guilty Thursday in Davenport to obstructing a federal employee, assistant U.S. Attorney Clifford Cronk, after the 2011 sentencing hearing for his son, Scott DeMuth. Timothy DeMuth could face a short jail term and fine when he is sentenced.

At the 2011 hearing, U.S. District Judge John Jarvey sentenced Scott DeMuth, then a 23-year-old University of Minnesota graduate student, to six months in prison. Rather than allowing him to surrender at a later date after returning to Minnesota, as his family and lawyer had expected, Jarvey heeded Cronk's recommendation and ordered Scott DeMuth taken into custody immediately.

Timothy DeMuth was "surprised and upset" that his son was imprisoned on the spot, and bumped shoulders with Cronk as the prosecutor tried to leave the courtroom, according to a plea agreement released Thursday. Timothy DeMuth then "intentionally stepped to the side, directly in front of Cronk, thereby opposing, impeding, intimidating, and interfering with Cronk as Cronk attempted to exit," the document states. An FBI agent quickly pulled DeMuth aside and escorted him to the lobby without incident.

"It doesn't take much to obstruct a federal officer, does it?" said Timothy DeMuth's attorney, John Moeller. "If you look at some of those cases, it's absolutely frightening how expansively the law is interpreted."

He said it is always emotional for parents to see their children sent to prison, but "the context of this case was a little more extreme." Moeller said the charge was reduced to a misdemeanor instead of a felony as part of the deal. Timothy DeMuth was released pending sentencing.

If accepted by Jarvey, prosecutor Richard Murphy said the plea agreement calls for DeMuth to face a recommended sentence of between 0 and six months behind bars under federal guidelines. The agreement says the fine range would be between $250 and $5,000.

His son's case was prosecuted in Iowa because he was initially charged in a 2004 attack on a University of Iowa research lab in which people in masks released hundreds of mice and rats, destroyed years' worth of research and caused roughly $500,000 in damage. The ALF, an extremist animal rights group, claimed responsibility.

Prosecutors started investigating Scott DeMuth in connection with the attack after authorities raided a Minneapolis home where he was living with other self-described anarchists who were protesting the Republican National Convention in 2008. He was indicted in 2009 and accused of being involved in the Iowa raid, despite little hard evidence linking him to the break-in.

Prosecutors eventually dismissed the charges against DeMuth in the Iowa raid as part of his agreement to plead guilty to misdemeanor conspiracy to commit animal enterprise terrorism in the ferret farm case. In that raid, vandals freed dozens of ferrets being bred as pets at a farm in Howard Lake, Minn.

At the 2011 sentencing hearing, Cronk called the raid "an act of cowardice done under the cover of darkness" that contributed to the farm's closure and destroyed its owner's livelihood. Cronk said an ALF statement taking credit for the raid and other evidence was found on DeMuth's computer.

The case against Timothy DeMuth was handled by Murphy, a federal prosecutor in Cedar Rapids, after the U.S. Attorney's Office for the Southern District of Iowa recused itself because it employs Cronk.