Harvard Medical School explosion: Arrests made, FBI says

It wasn’t immediately clear if the two men had retained counsel who could speak on their behalf.

Both men were arrested Tuesday morning and were slated to make their initial appearance later in the day in US District Court in Boston, officials said.

Surveillance footage at the building allegedly captured the pair walking toward the medical school campus around 2:23 a.m. wearing face coverings and dark clothing, the statement said.

They were allegedly captured one minute later on surveillance lighting what appeared to be roman candle fireworks, officials said.

Around 2:33 a.m., the statement continued, the two were allegedly spotted climbing over a chain link fence into a construction area surrounding the building. Minutes later, authorities said, they were allegedly seen climbing scaffolding besides the building to gain access to its roof.

Around 2:45 a.m., prosecutors said, campus police officers received an alert of a fire from an explosion on the building’s fourth floor, which houses a lab in the school’s Department of Neurobiology.

Authorities said additional surveillance footage allegedly captured the suspects on the fifth floor between 2:45 a.m. and 2:50 a.m. before they left the premises through a first-floor emergency exit and fled in opposite directions.

Investigators, the statement said, determined an explosive believed to be a large commercial firework had detonated in a wooden locker on the fourth floor.

“Analysis of the explosive is ongoing,” the statement said.

Shortly before 3 a.m., prosecutors said, Cardoza was allegedly seen on video surveillance sitting on a bench in the area, removing his trousers and placing them in a trash bin.

And beginning around 3:09 a.m., Patterson was allegedly seen on surveillance at the nearby Wentworth Institute of Technology campus intermittently running between buildings and trying to enter a dorm when a passerby let him in, according to the statement.

It said Patterson charged his phone at the attendant’s desk, and that he could be seen talking on the device around 3:23 a.m.

Roughly 17 minutes later, he was allegedly seen on surveillance exiting the dorm “to meet up with Cardoza and a third individual,” officials said.

At 3:49 a.m., after allegedly failing to gain entrance to another Wentworth dorm, they were spotted walking toward the Massachusetts College of Art and Design campus, the statement said.

“There, surveillance footage allegedly captured Patterson, Cardoza, and the third individual walking along Huntington Avenue,” the release said. “In the video, Patterson has allegedly removed his sweatshirt as well as his sweatpants, and is seen stuffing his sweatpants into his shorts.”

Cardoza, officials continued, “is allegedly seen still wearing a dark hooded jacket and black sneakers with only shorts or boxer shorts.”

Witnesses allegedly told investigators that Patterson and Cardoza had been visiting Wentworth for “Halloween social activites,” the statement said.

The release contained no information about a possible motive.

By Sunday, cleanup at the Goldenson Building was underway, and school officials said it would be back to functioning normally by Monday.

“The small section of the fourth-floor hallway where the explosion took place has been cleared and is fully operational,” George Daley, dean of the faculty of medicine, and Lisa Muto, executive dean for administration, said in a message to the medical school. “There was no structural damage to the building, and all labs and equipment remain intact.”

The school has maintained vigilance on potential attackers given its high profile and tension with the Trump administration.

Earlier this year, the university said it would pay security expenses for Harvard Hillel, a Jewish campus organization, amid fears of antisemitic violence.

Harvard was also targeted by a bomb threat in 2023.

A New Hampshire man was sentenced last year to three years of probation after he was found to have brought a hoax device to Harvard’s Science Center Plaza in Cambridge in 2023. Investigators later found he had unwittingly been recruited to do so after answering a Craigslist ad, in a scheme allegedly orchestrated by someone else, who later called the university demanding a large amount of cryptocurrency.

Material from prior Globe stories was used in this report. This story will be updated.

Travis Andersen can be reached at travis.andersen@globe.com. Sean Cotter can be reached at sean.cotter@globe.com. Follow him @cotterreporter.