DENVER (AP) – A former air traffic controller accused of planting homemade bombs outside the Colorado homes of four co-workers and a Federal Aviation Administration official pleaded guilty Friday and now could get 20 years in prison.

Robert Burke, 54, pleaded guilty to a charge of malicious damage to a building used in interstate commerce.

U.S. District Judge Robert Blackburn said the charge is punishable by five to 20 years in prison and a fine of up to $250,000. Prosecutors said they will recommended a term of 10 years when Burke is sentenced on Feb. 2.

Steve Sherwood, who found one of Burke’s bombs next to a bush that crews defused, said the sentence wouldn’t be long enough.

Burke was arrested in Utah in April, a month after authorities say he planted the bombs outside the homes in Grand Junction in western Colorado. Three exploded and two were defused. There was minor property damage, but no injuries.

Burke had worked for Serco Group PLC, a British company that staffs air traffic control towers at airports in Grand Junction and 55 other locations. He was fired in 2004 after working for Serco for four years.

An arrest affidavit said the Grand Junction homes that Burke targeted belonged to people who had provided information that Serco considered in determining whether to fire him.

The federal Bureau of Alcohol, Tobacco and Firearms has said the Grand Junction bombs were similar to a device that exploded at Serco offices in Murfreesboro, Tenn., in February, and one that caused a fire at a home in Derby, Kan.

Under the plea agreement, the government will not file charges in Kansas or Tennessee.

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