Bergdahl was questioned at Fort Sam Houston in San Antonio, where he has been staying since returning to the U.S., said his attorney, Eugene R. Fidell.
"Sgt. Bergdahl answered all questions put to him. The interview is proceeding. It has been a productive expenditure of time," Fidell said in a telephone interview during a break in the questioning. Fidell declined to comment on what specific questions Bergdahl was asked.
Lt. Col. Alayne Conway, an Army spokeswoman, said Bergdahl was advised of his rights under Article 31 of the Uniform Code of Military Justice. Article 31 pertains to individuals being informed of the nature of the accusation against them and says that they do not have to make any statement to investigators.
"This in an ongoing investigation; the investigating officer has 60 days from his appointment to conclude his investigation; however, he can request additional time if he feels it is necessary," Conway said in an emailed statement. She did not respond to an inquiry about what type of questions investigators asked.
Maj. Gen. Kenneth R. Dahl, who is heading the probe into the 28-year-old's disappearance, questioned Bergdahl on Wednesday, Fidell said.
A well-known lawyer and military justice expert who is currently a visiting lecturer at Yale Law School, Fidell described the setting of Bergdahl's interview as "a comfortable environment," a room with a sofa and a couple of chairs. He said there were four people in the room, the interview was being recorded and that they were taking breaks throughout the day.
It was not immediately known how long the interview would last. But Fidell said he expected this would be the only interview Bergdahl would be giving as part of the investigation.
"There is no reason to think there will be more than one," he said.
The Idaho native was freed by the Taliban May 31 in a deal struck by the Obama administration in which five senior Taliban officials were released from detention at Guantanamo Bay, Cuba. Bergdahl had disappeared from his post in Paktika province in eastern Afghanistan on June 30, 2009. Some ex-members of Bergdahl's former unit have labeled him a deserter, asserting that he chose to walk away and saying some were wounded or killed looking for him.
The investigation's findings will help determine whether Bergdahl is prosecuted for desertion or faces any other disciplinary action.
Bergdahl had been receiving care at Fort Sam Houston since returning to the United States on June 13. He was treated at Brooke Army Medical Center at the fort but was later shifted to outpatient care at the military base.
Earlier this month, the Army announced Bergdahl had been given a desk job, ending the formal phase of his transition from Taliban prisoner to not-quite-ordinary soldier.
Bergdahl has not commented publicly on the circumstances of his disappearance, and the Army has made no charges against him.
It is unknown if Bergdahl's family has seen him since his return to the United States. Army officials have said because of a request by Bergdahl's family for privacy, they cannot comment on that matter.