A New Hampshire man pleaded guilty Wednesday for his role in a “series of extortionate bomb threats” against Harvard University in April, the Justice Department announced.

William Giordani, 55, pleaded guilty in federal court in Boston to a count of concealing a federal felony. He was arrested in May and indicted by a federal grand jury in June.

The initial charge was dropped in exchange for Giordani’s pleading guilty in federal court to knowing about a felony and not reporting it to authorities, his lawyer told NBC Boston.

According to the Justice Department, on April 13, Giordani placed a large tool bag in Harvard’s Science Center Plaza, which contained a locked safe holding fireworks and wires. Students and other people were gathered nearby.

Then, a person using a voice-changing app called Harvard police to tell them that the caller had placed three bombs on campus.

The caller told police that if they did not transfer an unspecified amount of bitcoin, the bombs would be remotely detonated, the Justice Department said in a news release. The caller repeatedly placed calls telling police them they were serious about the attacks and where to find the first of the bombs — in the Science Center Plaza.

Upon finding the bag in the plaza, campus police issued an emergency evacuation order for the area and nearby buildings, the Justice Department said, adding that a Cambridge police bomb squad disabled the device and that no others were found on campus that day.

Investigators said they found that Giordani was recruited to join the scheme from an ad on Craigslist.

The Justice Department said that once he knew about the ploy, he “had an obligation” to report it. Instead, “he deleted incriminating text messages, told his girlfriend not to speak to anyone about it and went on the run from police,” the Justice Department said.

Giordani faces up to three years in prison and one year of supervised release for the felony charge. His sentencing is set for April 25.