A 27-year-old District man pleaded guilty Wednesday and admitted to making two separate, false bomb threats against Amtrak, officials said.

Michael Jerome Dennis admitted to making threats in telephone calls to Amtrak's National Communications Center on Nov. 30 and Jan. 19, according to the U.S. Attorney's Office. The calls each warned of a bomb going off at the New York Avenue NE bridge just north of Union Station. Dennis was working for a contractor at a site near the bridge at the time, and officials said that every Amtrak train from the Northeast Corridor that goes in and out of Union Station passes under the bridge.

Police searched the bridge and surrounding area after each threat. Six Amtrak trains were delayed over the course of the two incidents, impacting over 1,000 rail passengers, officials said.

The charge that Dennis pleaded guilty to specifically related to the Nov. 30 threat. It carries a likely sentence range of 18 to 24 months in prison, and a maximum of life in prison. Dennis is scheduled to be sentenced on Nov. 9.