MICHAEL CASEY BOSTON — Two Massachusetts men avoided jail time on Thursday after they earlier had pleaded guilty to setting off fireworks at an empty Harvard Medical School building, an incident that sparked a huge law enforcement response and increased anxiety on the college campus.

Federal officials say 19-year-old Logan David Patterson and 21-year-old Dominick Frank Cardoza were in the Boston area for college Halloween parties last year when they broke into Goldenson Building, set off a firework before dawn and then fled. No one was injured.

The two pleaded guilty in April to conspiring to damage a building using a large commercial firework. On Thursday, they were each sentenced separately to three years of probation, 300 hours of community service and a fine of $28,517 to be paid by the pair.

“I believe the harsh consequences that flowed from this conviction are a sufficient deterrent,” U.S. District Judge Angel Kelley said in denying a government request for six months of home confinement for the pair. A spokesperson for Harvard did not immediately respond to a request for comment.

Along with the probation and fines, the pair will have to write a letter apologizing to Harvard. At his sentencing, Patterson also apologized in court. “This was a very serious act. At the time, I thought my actions were harmless and they turned out to be much bigger.”Outside court, the lawyer for Cardoza, Stefan Rozembersky, said the sentence was fair given the circumstances behind the explosion. Neither of the defendants had a criminal record and both are working, one for a general contractor and the other doing landscaping.

“This was not a terrorist attack. This was not a coordinated attack against the government or aimed at Harvard; this was a couple of kids with firecrackers, not even bombs,” Rozembersky said, adding this was “mischief that went way out of control.”

Despite avoiding jail time, Rozembersky said the sentence still carries significant consequences. “It’s not without severity,” he said. “Having this felony record is going keep them from having some things in life and harm them for a long time.”Witnesses said the defendants were visiting the Wentworth Institute of Technology for Halloween activities, including parties at area schools. On the morning of the blast, surveillance footage captured the two walking toward the medical school building wearing face coverings. Witnesses said the pair chose the building because it looked abandoned and got into it via the roof by climbing up scaffolding, the charging document states.

The pair lit a Roman candle outside of the building and placed a cherry bomb inside of a locker in the building, where the device exploded, according to the charging document. Harvard police said an officer responding to the fire alarm saw two people running from the building.

“The defendant committed a serious offense, even if that offense was motivated by immaturity and revelry rather than more serious intentions to cause damage or fear,” prosecutors wrote in the government’s sentencing memorandum. “The defendants trespassed on a university building in the middle of the night wearing face coverings, exploded a firework that caused significant property damage and public alarm, and fled the scene.”The two could have faced a sentence of up to five years in prison, three years of supervised release and a fine of up to $250,000.