BOSTON, Nov 4 (Reuters) - Two Massachusetts men visiting

Boston area colleges on Halloween night when numerous parties

were underway have been arrested and charged with causing an

explosion over the weekend at Harvard Medical School's campus,

authorities said on Tuesday.

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 that drew national attention.

Police and the Federal Bureau of Investigation 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," U.S. Attorney Leah Foley

told reporters during a press conference.

Ted Docks, head of the FBI's Boston division, said no one was

hurt and property damage was limited, but he noted that "setting

off an explosive device inside a locker at an institution geared

toward higher education is not some harmless prank."

Lawyers for Patterson, of Plymouth, Massachusetts, and Cardoza,

of Bourne, Massachusetts, could not be immediately identified.

According to charging documents, surveillance cameras captured

two men later identified as Patterson and Cardoza shortly after

2 a.m. 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 its roof, 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 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.