BEVERLY — A hearing in the case of a Tuck's Point resident charged with keeping four homemade bombs, an unlicensed handgun and an assortment of ammunition in his luxury condo got underway yesterday with testimony from a veteran drug detective.

Robert Cohn, 56, a paralegal and case manager for a Woburn law firm, had been under surveillance after police got a tip that he had been peddling heroin, methadone and OxyContin, Detective Tom Nolan said.

After a series of undercover purchases from Cohn, Nolan said, he applied for a search warrant for Cohn's condo at 117 Water St., Unit 24.

That search, conducted on March 13, turned up a list of items that also included fake identification with Cohn's photo and another person's name and four small bags of heroin in Cohn's pockets. Cohn also had a surveillance camera set up in a window of the condo.

While police were booking Cohn, Nolan testified, he received a cell phone call and a text message from someone looking to buy "one brown and four regs," which police believe are references to heroin (which is brown) and regs, or 10-milligram methadone tablets.

Cohn repeatedly whispered to his lawyer, Cesar Archilla, during the hearing, and when Archilla began his cross-examination of the officer it appeared that Cohn had been giving the lawyer questions to ask.

But the defense hit several dead-ends.

"You've known Mr. Cohn since the 1980s, isn't that true?" Archilla asked Nolan, who has been a police officer for 10 years — and who would have been in high school in the 1980s.

Nolan said he didn't know Cohn until he made a traffic stop about five years ago.

"Do you have a sister who is familiar with Mr. Cohn?" Archilla asked. But when Nolan explained that his sister is even younger than he is, Judge Michael Lauranzano intervened.

"Maybe it's a case of mistaken identity," said the judge. "Let's move on."

Archilla also tried to question Nolan about an ongoing legal battle between Cohn and the condo association at Tuck's Point, which took him to court in 2001 over Cohn's decision to replace the windows in his unit. The condo board has been forced at times to hire police details for condo association meetings. Prosecutor James Steinberg objected to the line of questioning, however.

The defense lawyer also tried to suggest that the tipster had given police the wrong information about where the drug activity was taking place, noting that police have been called to the unit downstairs from Cohn's about a tenant who has a drug problem.

As for reports of visitors to his condo at all hours, Archilla suggested that as a paralegal and case manager for a law firm, Cohn is required to "work all kinds of hours."

The hearing will resume today with testimony from Sgt. Michael Cassola, who was also involved in the investigation.