WASHINGTON  Army investigators are broadening their inquiry into the recent disclosure of classified military information to include friends and associates who may have helped the person they suspect was the leaker, Pfc. Bradley Manning, people with knowledge of the investigation said Friday.

Two civilians interviewed in recent weeks by the Army’s criminal division said that investigators were focusing in part on a group of Private Manning’s friends and acquaintances in Cambridge, Mass. Investigators, the civilians said, apparently believed that the friends, who include students from the Massachusetts Institute of Technology and Boston University, might have connections to WikiLeaks, which made the documents public.

It is unclear whether the investigators have specific evidence or are simply trying to determine whether one person working alone could have downloaded and disseminated tens of thousands of documents.

The Army has charged Private Manning with disclosing a classified video of an American helicopter attack to WikiLeaks, as well as more than 150,000 classified diplomatic cables. Military officials said Friday that the private was also the main suspect in the disclosure to WikiLeaks of more than 90,000 classified documents about the Afghan war, some of which were published this week by The New York Times, the German magazine Der Spiegel and the British newspaper The Guardian.