A prominent AIDS researcher linked to a man charged with gathering an arsenal of bombs and weapons in a Brooklyn Heights apartment after allegedly painting swastikas on area synagogues has declined to cooperate with police, according to police sources.

Immigration and Customs Enforcement officers picked up the researcher, Michael Clatts, at John F. Kennedy International Airport yesterday morning as he was returning from Vietnam, where he had been conducting a research project for the National Institute on Drug Abuse.

Mr. Clatts’s roommate, Ivaylo Ivanov, 31, was arrested over the weekend after an arsenal of pipe bombs, bomb-building equipment, and firearms was discovered in an apartment at 58 Remsen St. that Mr. Clatts owns. Police officials have said Mr. Ivanov confessed to the swastika incident after several hours of police questioning, and he was later charged with that crime as well.

Customs officers took Mr. Clatts to the Downtown Brooklyn precinct, where he refused to speak with detectives working on the case. Instead, he requested his lawyer be called and was later released.

The lawyer, Louis Klieger, said he could not comment on the case.

Police have said they do not suspect Mr. Clatts of being involved in either the hate crime incident or the arsenal of guns and bombs found in his apartment, and said it is unlikely that he would be charged with any crime.

A neighbor who lives in the building, James Robinson, said Mr. Clatts had sent out an e-mail apology message on Monday to all of the residents of the building.

“He said that he was disturbed about the news he was getting,” Mr. Robinson said. “He was very apologetic, and said that he had absolutely no idea about all of this.”

Mr. Ivanov, known as Ivo to his neighbors, has alternately explained the arsenal by saying he needed it for protection and that he was planning to use the bombs for fishing. He has also claimed to be Jewish.

Several neighbors in the building said they believed that Mr. Clatts would have been unaware of his roommate’s alleged involvement in the crimes. Mr. Clatts travels often for his work, his neighbors have said, and he was not believed to be in the apartment this week when the arsenal was found.

The e-mail from Mr. Clatts also said that he was in a “remote country” and would be coming back soon, according to Mr. Robinson, who said he notified police about the e-mail message.

Mr. Clatts is a medical anthropologist employed by the National Development and Research Institutes and is also affiliated with Columbia University. He is studying HIV risk among young drug injectors in Vietnam, according to the National Institute on Drug Abuse’s Web site, and he was one of the first social scientists to begin research on AIDS in the early 1980s. A researcher at the institute who has written several papers with Mr. Clatts declined to discuss his colleague yesterday, citing the organization’s policies, and the executive director of the organization did not return several calls and an e-mail request for comment.

A spokeswoman for Columbia’s Mailman School of Public Health noted this week that although he is listed as an associate professor there, he is not paid and does not teach at the school.