And now, we at abc mark a milestone in america's longest war, afghanistan. Now, entering its 12th year. A milestone of sacrifice. The ap says 2,000 u.S. Troops have now died in combat there. And abc's... See More
And now, we at abc mark a milestone in america's longest war, afghanistan. Now, entering its 12th year. A milestone of sacrifice. The ap says 2,000 u.S. Troops have now died in combat there. And abc's michael boettcher has been covering the war in aft afghanistan from the beginning, living among american troops. And the military says more than any other reporter, including a full year with the 101st airborne. And, tonight, he has a report on this crossroads and the road ahead. Reporter: There is not one face to this grim milestone. There are 2,000. Americans who gave their lives in this nation's longest war. Soldiers like alejo thompson, a son of yuma, arizona, husband and father of two, who was killed last may by an afghan soldier he was mentoring -- a so-called green on blue, or insider attack. We traveled to the scene to speak to sergeant joshua danison who witnessed the attack. His is the first public eyewitness account of an insider attack. We woke up one morning to some gunshots being fired. It was an afghan national army soldier. The shooter actually walked up lieutenant thom p sop, who had already been wounded, and shot him a second time. Reporter: Thompson's killer escaped after the attack and, in this taliban video, is shown being given a hero's welcome. Now the men, who trust each other with their lives, wrestle with betrayal. There were comments that we don't trust them, we don't want to be around them. We don't want to partner with them any more. But to overcome that, we have to look at it as a mission. Reporter: But for the troops, there is worry. mission now. And will be until the last american troops leave afghanistan in 2014. I hope that's bread and not an ied. Reporter: The sounds of a little test fire catches everyone's ear. Hardened warriors on edge over those insider attacks. And our mike boettcher is here right now. So, mike, what are they saying about 27 more months until the drawdown, the year ahead? Reporter: Well, bottom line is, they don't want the last 11 years to be for nothing, so, they press on to honor the fallen. But this next year, the most critical of all. So, they are at war, this next year, in a whole new way. Reporter: With a new threat. And you'll be covering it, i know. Thank you so much.
This transcript has been automatically generated and may not be 100% accurate.