In separate appearances Wednesday in U.S. District Court in Akron, Connor Christian Stevens, 20, of Berea, Ohio; Douglas L. Wright, 26, of Indianapolis; and Brandon L. Baxter, 20, of Lakewood, Ohio, all pleaded guilty to conspiracy to use weapons of mass destruction, attempted use of weapons of mass destruction and malicious use of explosives, the (Akron) Beacon Journal reported.
A fourth man charged in the incident, Joshua S. Stafford, 23, of Cleveland, remains in federal custody undergoing psychiatric evaluation. He has not yet been tried.
A fifth man, Anthony Michael Hayne, 35, also of Cleveland, pleaded guilty in late July to conspiracy to use weapons of mass destruction and two additional federal explosives charges.
He faces a prison sentence of 14 to 19 years after agreeing to testify against the others.
All five were arrested April 30 by the FBI, who alleged they tried to blow up the 1,100-foot-long bridge using bombs supplied to them by an undercover informant.
The bombs were fake and the bridge was not damaged.
Defense attorneys for the three who pleaded Wednesday said they would argue for minimum mandatory sentences because they felt the plot was orchestrated by the FBI.
Terry Gilbert, who represents Stevens, described the informant as a man "with an outrageous criminal background" who had to guide the men through every step of making and placing the bombs.