Spec. Adam Winfield considered being a whistleblower, as shown in the documentary “The Kill Team.” Instead, he ended up on trial and fearing for his life. (Dan Krauss/Oscilloscope Laboratories)

In 2010, Army Spec. Adam Winfield was at a crossroads. Members of his platoon had killed an innocent boy farming in Afghanistan and planted a grenade on his body. In a message to his father, Winfield asked whether he should become a whistleblower, which might put his life in danger, or just lie low and try to avoid getting pulled into the orbit of his homicidal staff sergeant.

“Why am I the only one that’s not okay with this?” he wrote.

And yet, months later, Winfield was facing murder charges. Just how Winfield got from point A to point B is the subject of Dan Krauss’s documentary “The Kill Team,” a disheartening look at the war in Afghanistan, the military justice system and what can happen when soldiers get bored in the desert.

The child’s death was only the beginning, and even after sending the message to his father, Winfield ended up in the thick of it. His father tried to report what his son had told him, leaving messages everywhere he could think of. He finally got through to a sergeant at Fort Lewis, Wash., who threw up his hands and said that Adam would have to take his accusations to his superiors. But given that his commanding officer was openly discussing killing Winfield, the specialist thought best to keep everything to himself.

Krauss focuses on Winfield and his parents leading up to the murder trial, but the director also gets access to a few others who were charged, as well as the man, Justin Stoner, who ultimately reported everything (and admits that he wishes he hadn’t). Winfield’s story is tragic — hinging on one moment he will likely replay in his head forever — but the interviews with the other men may be more telling. Their mindsets were disturbingly similar and they admit, with shocking frankness, that their boredom, coupled with an intense distrust for all Afghans (“Nobody’s innocent,” one of them justifies), turned into a killing spree.

If Krauss offers up a clear villain in this story, it’s the men’s staff sergeant, Calvin Gibbs, who was the mastermind. All you need is a “drop weapon,” he told his subordinates, and then you can pretty much kill with impunity. Gibbs also had some sick tendencies, such as collecting fingers of victims that he planned to string together into a necklace and tattooing skulls on his leg to represent each of his kills.

Gibbs isn’t interviewed in the film, which makes him an easy target, but there also was more evil at play, especially given the number of people who either participated in or knew about the killings. There’s a psychological element here that Krauss leaves frustratingly unexplored, even as Stoner says, in his smug way, “I don’t care what the military wants to say, but this goes on more than just us. We’re just the ones who got caught.”

“The Kill Team” is expertly edited, at one point overlaying interviews with the men who participated in the war crimes with B-roll of infantrymen milling about, weapons in hand. And it’s all set to a brilliantly spare and evocative soundtrack. It’s a beautiful way to lose faith in humanity.

★ ★ ★

Unrated. At Landmark’s E Street Cinema. Contains strong language and grisly images. 79 minutes.