Two days after a fire forced the evacuation of Matthews Hall, causing no damage, University police and the Cambridge Fire Department are attributing the incident to arson.
Officials said they are now conducting an investigation, but they declined to say whether they had any suspects.
A Matthews resident extinguished the fire, which started in a pile of trash late Monday night, before firefighters arrived on the scene.
Philip Rosenblum '89 said that he discovered the fire on the second floor of the freshman dorm shortly before midnight and put it out just as smoke triggered the building's alarm.
"I think it was more or less a malicious act," said Cambridge fireman Michael Edwards. "Various other small fires were set along the walls. They were all out by the time we came," he said.
Matthews resident Michael Metzger '89 said he saw ashes and charred paper on the floor of the second-story bathroom before the alarm began ringing.
Matthews residents initially reacted to their first alarm of the year with confusion, they later said.
"At first, I thought it was just somebody making popcorn," said Rudy Ruiz '89.
Said Cathy Green '89, "I was asleep. When the alarm rang, I hit the snooze button on my clock, but the sound didn't stop."
Another evacuee, Paul Sforza '89, said he responded immediately. "Out of the corner of my right eye, I saw orange flame. I felt heat, so I ran like hell."
Other Matthews residents found the fire more exciting than threatening. "We finally got to use the fire escape," one resident said.