Intense focus on the army sergeant freed from the Taliban. What we know about the note he wrote before leaving his base. After years of studying those images, his appearance changing and uniform... See More
Intense focus on the army sergeant freed from the Taliban. What we know about the note he wrote before leaving his base. After years of studying those images, his appearance changing and uniform replaced. At times you can see one of his captors with him. Tonight we learned there was a final video we didn't see that troubled U.S. Authorities. What was in it? Martha Raddatz with what she's learning tonight. Reporter: The army tonight preparing to investigate. The chairman of the joint chiefs saying Bowe bergdahl is innocent until proven guilty but that they will be looking at potential misconduct in his disappearance and capture as soon as he is recovered enough to talk. A senior defense official tells ABC news that bergdahl wrote a note before disappearing saying he was disillusioned with the mission and that an army investigation concluded he had walked away from his remote base on his own. Fellow soldiers now saying there were signs. He wanted to know how he could send his computer and some of his belongings home and he asked me how he could get money. Reporter: The officials say they are not certain how he ended up with the Taliban, but that bergdahl, who loved ballet and motorcycles, was so idealistic he may have thought he could bring the two sides together. In the first hostage video bergdahl was even asked about soldiers who go awol. They're deserting because they don't want to be here because they know that this is wrong and they just want to go home to their families. Reporter: And it was those videos that U.S. Officials were watching closely. Images of bergdahl appearing calm and seemingly grateful at his treatment gradually give way to a face full of fear and panic. Release me, please. I'm begging you. Reporter: But we learned today there was another video released this year and only seen by the U.S. Government that sparked the greatest concern. An official telling ABC news that the once fresh soldier was clearly becoming frail and disengaged. That is why the urgency said the -- after bergdahl once the Taliban was secured. As for his desertion that is a crime punishable by jail time. But still tonight no one we are speaking to believe that is on the table given his years of captivity. As you heard, the U.S.
This transcript has been automatically generated and may not be 100% accurate.