The agents got to the Gun Tower at 2:45, and for the next two hours and 45 minutes they performed a detailed examination of the third floor, including mapping the locations of the blood and gore, and taking measurements of the gun table, the chair, and the window. Nothing in that room was supposed to escape their attention. They were unable to find the bullet or fragments of it, even when they returned the following morning with a metal detector. In retrospect, on some of the simplest matters involved in detailing a crime scene, they made fundamental errors. They got the dimensions of the gun table wrong. This was an important miscalculation, because it allowed for subsequent miscalculations to stand. Furthermore, when the agents came to the hole in the Plexiglas window that Lieutenant Faust clearly described as fragmented, one of them wrote: “Based upon the point of impact, possible trajectory of the projectile, the size of the hole in the Plexiglas, and the lack of cracks or stress marks around the hole, it did not appear as though the hole was made by a small arms round.” That was it. They never returned to the subject, even after Faust, their fellow policeman, submitted his observations. Ten years later, under pressure from James Culp, the C.I.D. produced photographs from the files that clearly showed a fractured and splintered hole.

After inspecting the tower, the agents went to Brown’s quarters, a scene that had been secured by Torres. There, in a plastic bag, they found 12 empty blister packs, each of which had contained 10 milligram pills of Valium manufactured by Roche Pharmaceuticals of Pakistan. The discovery was significant. This was a high-quality industrial product that was coming across the nearby border, and it suggested access to more than an artisanal level of Pakistani narcotics. Three more blister packs appeared during a second search the following afternoon.

The military suspected that someone at the base was providing soldiers with an ample supply of drugs. Later that year, Culp was told, the C.I.D. formally named two unidentified soldiers as suspects in a drug operation at Asadabad. After one of the soldiers invoked his right to legal counsel, however, the initiative was dropped. The optics would certainly have been bad for the army: Asadabad as a staging point for Pakistani narcotics flowing unchecked to U.S. troops throughout Afghanistan. On the base, Valium abuse was so widespread that a few months after Brown’s death, Culp learned, all 120 soldiers in his battery were quietly pulled from their individual barracks and forced to sleep in open bays, to deprive them of privacy for the remainder of their tour. As often occurs, the army preferred to avoid embarrassment rather than to identify and prosecute the perpetrators.

However Matthew Brown died, the existence of a drug ring at Asadabad could have provided a motive to kill him. He was unreliable, a whiner who wanted out, a courier who knew all sides, a kid getting high on his own supply. On the morning of his death, his condition in the Gun Tower could have landed him in the hospital, where questions would have been raised and he might have begun to talk.

None of this proves that Brown was murdered. The inner life of even those closest to us can be secret, and some people commit suicide without warning, leaving their families bewildered. It is completely possible that Brown took his own life. It is also possible that everything Brown told his mother about the drug ring was untrue, and that Torres and Jackson were guilty of nothing more than inadvertently violating standard crime-scene protocols. The point is not that we know Brown was killed. The point is that we cannot be certain how he died, because the C.I.D. investigators seem barely to have considered any possibility other than suicide, even after they stumbled upon evidence of a drug problem at Asadabad. Their greatest concerns appeared to be Brown’s habitual drug use and the strange disappearance of his wallet. It was not found after careful searches of his quarters and the tower, as well as two searches of his body. Yet it mysteriously materialized inside the body bag after it arrived at Bagram. Had someone been worried about what it might contain? Jackson had accompanied Brown’s corpse on the flight from Asadabad. The investigators questioned him but drew no larger conclusions, and ultimately shrugged it off. Later, when Senator Barbara Boxer inquired about the missing wallet, the army told her—incorrectly—that the C.I.D. agents had found it as soon as they arrived at Asadabad.

VI. FORENSIC RECONSTRUCTION

The culmination of their investigation occurred on the seventh and final day of their visit to the base. It was May 18, three days after the medical examiner in Dover had declared Brown’s death a suicide. On that day, several significant scraps of evidence came to light. From additional questioning, for instance, it became clear that the use of narcotics on the base was far more common than had at first been acknowledged in written statements. Had the C.I.D. fully investigated the implications, it might have come to a more thorough and convincing explanation of Brown’s death—even if it was a suicide. Instead the investigators caught a flight out that evening, leaving behind an unfinished job and questions that remain to this day.