Months after a pipe bomb damaged three rooms at the Yale Law School and police raided four local homes in search of evidence, authorities have made no arrests and say they have no primary suspect in the bombing.

Within a month of the bombing, law enforcement officials searched the Hamden homes of Benjamin Johnson, a former employee of Yale’s Beinecke Rare Book and Manuscript Library, and Norman Yarvin, 32, a former employee of the Yale computer science department. Authorities also searched the dorm room of Denis Delja LAW ’02 and the Branford home of Vincent Pergolotti Jr., 37, who worked for the Law School’s library more than 10 years ago before he was convicted of arson in 1993.

After the rash of activity this summer, however, authorities have not conducted any additional interviews or searches in recent weeks.

“In these types of incidents, the investigation is a very painstaking investigation, so it does take some time,” U.S. Attorney Kevin O’Connor said. “It isn’t to be expected that the investigation will be completed in a day or a week or a month.”

Students returning to the Law School this semester will see few signs that the incident occurred at all, according to an e-mail sent to law students by Yale Law School Dean Anthony Kronman. All three damaged rooms were opened for student use this week, Kronman said.

“Over the summer, the damaged rooms were fully repaired and restored to their original condition, with a few modest improvements along the way,” Kronman said.

Kronman said the investigation into the incident was ongoing and expressed confidence that those involved would be found.

Johnson was convicted last year of stealing millions of dollars worth of artifacts and documents while he worked at the Beinecke library the summer before. In June, he was arrested again when his parole officer found two passages about explosives in a notebook Johnson kept in his backpack, Johnson’s lawyer Penn Rhodeen said. Johnson was released six days later.

“[The FBI] looked into whatever they’ve looked into, and then he was released,” Rhodeen said. “He was totally cooperative.”

In searching the Law School following the bombing, investigators discovered firearms in the Delja’s dorm room. The firearms, said Delja’s mother Beatrice, were used by Delja in war re-enactments. After interviews with law enforcement, the firearms were returned.

“It was all fine and taken care of,” Beatrice Delja said. “He graduated and moved on.”

Yarvin became involved in the bombing investigation after his house was burglarized, when police investigating the burglary noticed that Yarvin had pipe and gunpowder and called the FBI. Yarvin, who was out of town during the burglary, said he was not notified of the search until he was called by a reporter from the New Haven Register.

“They were clearly looking for some specific things,” Yarvin said. “They took drill bits, grinding wheels, things that would leave a mark on a pipe bomb.”

Yarvin said the gunpowder was used to reload his collection of guns and he denied any involvement in the bombing. Though he said the police have not returned his things, he has not been interviewed recently and is no longer a top priority in the investigation.

Yarvin said he did not have any major complaints about authorities’ handling of the search.

“It’s the government. They’re always slow,” Yarvin said. “They could cause a fair amount of trouble, but I didn’t read that in their attitude at all.”

Pergolotti’s lawyer, Norman Pattis, expressed more frustration with the investigation. Pergolotti has a history of trouble with Yale police, the New Haven Register has reported.

“Just because he had a problem with Yale doesn’t make him public enemy number one and it’s time for Yale and everyone else to grow up,” Pattis said.

Despite the setbacks and dead ends, O’Connor said he was not discouraged by the investigation.

“I’m very pleased with the progress we’ve made,” O’Connor said. “We’re very confident that we will find the person or persons involved with this, and we will charge them.”

New Haven police and FBI agents were not available for comment because of a gag order imposed by the U.S. Attorney’s office. After initial cooperation between federal and local authorities, New Haven police are no longer actively pursuing the case. New Haven police spokeswoman Bonnie Winchester said she is not aware of any police officer working steadily on the case and that the FBI is no longer sharing leads.

“Kind of the way it was put to us is that ‘we don’t trust you so we’re not going to tell you anything,'” Winchester said.