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The blast on the research building’s fourth floor early Saturday morning caused no injuries and little property damage. Here’s what to know. In an affidavit, FBI special agent Erin O’Brien laid out a timeline of Cardoza and Patterson’s night on Oct. 31 into the early morning hours of Nov. 1, based on witness statements and surveillance footage. The pair arrived at Wentworth Institute of Technology around 8 p.m., meeting up with several people who were going out to what the FBI agent describes as “Halloween social activities.” One person they went out with told police the pair had split off as the night grew late, saying they were headed to a party by Tufts University. Cameras began to catch them in Longwood after 2 a.m., according to O’Brien. Footage on Longwood Avenue allegedly captured the pair walking toward the medical school campus around 2:23 a.m. One of the men, she wrote, was clad in a balaclava, a brown sweatshirt, tan pants, and white Crocs, while the other was in a blue mask, a dark jacket, and plaid pajama pants. Around 2:24 a.m., they set off what appear to be Roman candle fireworks outside, footage showed. A few minutes later, video footage from the Goldenson Building at 220 Longwood Ave. shows them climbing a chain-link fence and hopping into a construction area, the FBI agent wrote. Then, at 2:36 a.m., the pair was spotted climbing scaffolding next to the building and getting onto its roof. At 2:45 a.m., police received an alert that there had been an explosion on the fourth floor of the building. They soon left the building, fleeing in opposite directions, according to video footage. The man in plaid pants — later identified as Cardoza — sat down on a bench and ditched the pants, taking them off and throwing them out in a trash bin, according to the FBI, citing more surveillance footage. Beginning around 3:09 a.m., Patterson had returned to Wentworth and, according to more video footage, was running between buildings, trying to enter. After he was able to get into a building and charge his phone, he met back up with Cardoza and a third person who is not federally charged with any crime related to the explosion. The trio tried but failed to get into another Wentworth dorm, footage shows, so they moved on to the nearby Massachusetts College of Art and Design campus, the FBI agent wrote. By that afternoon, the pair headed back out of town, on their way to the University of Massachusetts Amherst to party, according to the documents. Federal agents arrested Patterson and Cardoza at their respective homes on Tuesday. Both men were charged with conspiracy to damage by fire or explosive, which carries a sentence of up to five years in federal prison upon conviction. As of now, it appears Patterson and Cardoza had little apparent motive for getting into the building and setting off a firework. No political motive was apparent in a seven-page probable cause affidavit, and US Attorney Leah Foley declined to speculate on any motive, saying the investigation remained in its early stages. The arrests have been touted by federal authorities, including FBI Director Kash Patel. “Great work @FBIBoston and partners - another win for our Joint Terrorism Task Force getting the job done,” Patel wrote on X. In a later post, Patel wrote: “FBI Boston’s Joint Terrorism Task Force, with Harvard Police and local partners, swiftly arrested two suspects in the Harvard Medical School explosion. This FBI will always act decisively to protect the public.” Material from previous Globe coverage was used in this report.
