Bergdahl, who was released in May after five years of captivity in a controversial prisoner swap, was read his rights under military law, notifying him that he is a potential defendant in a criminal case.
The questioning was "cordial" over two days by Major General Kenneth Dahl, who will now make a recommendation to the Pentagon on what punishment, if any, Bergdahl should face, Bergdahl's attorney, Eugene Fidell, said in an interview.
Some of his fellow soldiers in Afghanistan have said Bergdahl deserted his post and the Pentagon appointed Dahl to recommend whether the soldier from Hailey, Idaho, broke any military laws.
Bergdahl was released in exchange for five Taliban prisoners from the U.S. prison in Guantanamo Bay, Cuba in a swap that triggered an outcry from critics of the Obama administration.
Fidell said Bergdahl answered every question posed to him openly and honestly though he could have refused to answer questions. Fidell did not say what questions were asked.
"He's made of pretty stern stuff," said Fidell, who would not disclose details of the questioning. "It was a piece of work that had to be done, and now it's done."
The appointment of a major general to investigate the case demonstrates the importance and sensitivity the military places on it, said retired Army Lieutenant Colonel Jeffrey Addicott and Greg Rinckey, a former Army Judge Advocate General officer.
Dahl is charged with trying to find out how Bergdahl came to be away from his post when he was captured by the Taliban.
Addicott, a former senior legal adviser to U.S. Army Special Forces, said Dahl has many options including recommending administrative punishment up to a general court martial.
"He can also recommend that he go through a medical disability retirement," Rinckey said, adding that he also could recommend Bergdahl leave the Army.
Dahl has until the end of next week to issue recommendations and could ask for an extension. The Army also could reject the recommendations.
Bergdahl completed a course of counseling and reintegration after his release and has been assigned to administrative work at Fort Sam Houston.