An Army private charged in the biggest leak of classified material in U.S. history is set to tell a military judge how he did it and why.

Pfc. Bradley Manning will answer questions Thursday from the judge who is considering whether to accept his offer to plead guilty to some charges.

Manning's only public explanation for giving classified material to WikiLeaks can be found in logs of an online chat with a confidant-turned-government informant. In those chats, Manning wrote that he engineered the leak because "information should be free" and he wanted "people to see the truth."

Even if a judge accepts his guilty plea, prosecutors can still pursue more serious charges against Manning. One charge is aiding the enemy, which carries a potential life sentence.