BOSTON, Nov 5 — Two Massachusetts men visiting Boston-area colleges on Halloween night when numerous parties were underway have been arrested and charged with causing an explosion at Harvard Medical School’s campus, authorities said yesterday.

Federal prosecutors alleged that Logan Patterson, 18, and Dominick Cardoza, 20, broke into a building housing Harvard research labs early Saturday morning and caused an explosion with a commercial firework.

Police and the Federal Bureau of Investigation (FBI) on Saturday announced they were investigating what the Harvard University Police Department said appeared to be an “intentional” explosion.

“Anxiety levels naturally rise when the public learns that an explosion was intentionally caused,” US Attorney Leah Foley said at a press conference.

Ted Docks, head of the FBI’s Boston division, said no one was hurt and property damage was limited, but added that “setting off an explosive device inside a locker at an institution geared toward higher education is not some harmless prank.”

Both Patterson, of Plymouth, and Cardoza, of Bourne, were released following an initial court appearance. Kevin Reddington, Patterson’s lawyer, said in an email that he was confident authorities would ultimately “see that this is far from a serious case with any malice.”

“These are two kids, no record,” Stefan Rozembersky, Cardoza’s attorney, said in a statement.

According to charging documents, surveillance cameras captured two men later identified as Patterson and Cardoza shortly after 2.00am on Saturday walking toward the Harvard Medical School campus while wearing face coverings.

Surveillance video showed them lighting Roman candle fireworks, climbing over a chain-link fence, entering a construction area surrounding Harvard’s Goldenson Building and then climbing scaffolding to access the roof, the charging papers state.

Harvard police minutes later received an alert of a fire alarm from an explosion on the building’s fourth floor, which houses a laboratory within the school’s Department of Neurobiology. The men then fled.

Authorities said the explosive detonated in a locker, and it is believed to have been a large, commercial firework.

Surveillance video captured Patterson after the explosion at Wentworth Institute of Technology in Boston and recorded him later meeting up with Cardoza. Students at Wentworth told investigators that both men had gone there earlier in the night for Halloween social activities and told some of them about their involvement in the explosion, according to court documents. — Reuters