One of five men charged with plotting to bomb an Ohio highway bridge made a surprise guilty plea Wednesday and agreed to testify against his co-defendants.

Anthony Hayne, 35, pleaded to all three counts against him in US District Court. His attorney, Michael O'Shea, said Hayne hopes to get leniency in return for his testimony.

Authorities have called the men anarchists. Investigators say the group planted what turned out to be a fake bomb provided by an FBI undercover informant on a bridge south of Cleveland and repeatedly tried to detonate it using text messages from cellphones.'

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The defendants could face life in prison if convicted.

Under the terms of the plea deal, Hayne will have the chance to avoid a life prison term. He could face 15 years to nearly 20 years in prison.

"I don't think any of these guys intended harm to human beings," O'Shea said. "I think they just thought this was a way of making some sort of political statement. But I'm relatively confident none of these people had any desires to actually hurt anybody."

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O'Shea said Hayne was a latecomer to the alleged plot and had the least standing to argue that he had been manipulated by an FBI informant.

The five had been associated with the Occupy Cleveland movement, part of a national demonstration last year against economic inequality, but organizers of the movement have tried to distance the group from the men. They say the five didn't represent it or its nonviolent philosophy.