Boston police discovered material that could be used to create a homemade bomb in a man’s East Boston apartment that was damaged in an explosion, prosecutors said Monday.
Investigators searched the Webster Street apartment and found a semiautomatic handgun, a Russian-made rifle, and more than 100 rounds of ammunition, Suffolk Assistant District Attorney Brian LeBlanc said. They also found chemicals used to make “black powder” and a sealed PVC pipe with a hole drilled into it.
“The configuration, according to bomb technicians on scene, is consistent with homemade, small PVC pipe bombs,” LeBlanc said.
The tenant, Tomas Mikula, 28, sustained second-degree burns in the blast, which happened around 12:40 Sunday morning. He was arraigned Monday from his hospital bed in the burn unit at Massachusetts General Hospital.
He pleaded not guilty to a number of weapons and explosives charges and was ordered held in lieu of $200,000 bail.
The apartment building sustained “major internal and structural damage” estimated at $50,000, LeBlanc said. Mikula suffered major burns to his legs, arms, and forehead and told police the explosion had originated in his second-floor apartment, LeBlanc added.
“He told officers that he went out to walk his dog, went up to his apartment, turned on his computer, and his computer and monitor exploded,” LeBlanc said.
Mikula’s court-appointed lawyer, Arthur Shabo, said it was unclear whether any other tenants had been in Mikula’s apartment around the time of the blast.
“There’s been no indication of where these people were or what apartment they were in,” he said.
Mikula is due back in court Aug. 6.
On Monday, shards of glass and crumpled-up police tape were scattered on the sidewalk in front of the building, and the windows on the second-floor apartment were boarded up.
Damage could also be seen on the ground floor of the building, where the overhead light in the foyer was broken and plaster had fallen from the ceiling, leaving the wooden slats exposed and a thick coating of debris on the floor.
Neighbors said they were relieved that no one else was hurt and expressed concern about Mikula’s alleged actions.
Suzi Meconi, 34, who lives in the apartment building next door, was not home when the explosion happened. When she and her family got back Sunday afternoon, they weren’t allowed into their apartment for hours. The incident was terrifying, she said, because her baby’s room is near to the site of the blast.
“Luckily there’s a firewall between the buildings,” she said.
She and her husband would occasionally see Mikula and say hello but did not know him well. They sometimes saw him walking his dog. Like other neighbors, she questioned what he was doing in his apartment.
“Playing with chemicals as a hobby?” she asked. “That is not a normal activity.”
Boston Mayor Martin Walsh expressed similar concern.
“What was the intention of having that type of material?” he asked. “It’s dangerous. You’re right in the middle of a residential community.”
In 2009, Mikula pleaded guilty to charges of identity fraud and larceny and received a two-year sentence, prosecutors said. Mikula was also convicted of a firearm charge in 2009 and several theft-related crimes between 2011 and 2014.
Travis Andersen of the Globe Staff contributed to this report.