For a crucial piece of evidence that it asserted would exonerate its personnel, the D.E.A. kept the video under tight control. The first time it was shown outside the agency was in May 2012, shortly after the shooting, when it was screened in a secure conference room for a group of congressional staff members.

The D.E.A. and State Department briefers controlled all the information, said Peter Quilter, a former staff member for the House Foreign Affairs Committee who attended some of the initial briefings. “It was very difficult to second-guess them.” He added: “They very simply misled the Congress. The video did not back up their story of what happened.”

In at least eight briefings over six months, and in multiple letters in response to senators and representatives, the D.E.A. maintained that the shooting was justified.

In June 2012, United States officials allowed a New York Times reporter to briefly view portions of the video, probably those shown to Congress. The officials pointed to blips in the grainy night-vision video, which they said were indications that the occupants of the passenger boat had fired on the team on the canoe. The Times described these flashes as less clearly visible than the ferocious series of shots from the canoe carrying the agents. The still-secret video was not definitive in supporting the D.E.A.’s version of events, The Times reported, saying that the video “answers some questions while raising new ones” about the operation.

The video was released to the public through the Freedom of Information Act, with the law firm Jenner & Block taking on the case pro bono. A federal judge ordered the release of the video in January 2016, and the agency appealed. In June 2017, an appeals court ruled against the D.E.A., and the agency released the video.

The video opens on the outskirts of Ahuas, around 1 a.m. on May 11, 2012. A propeller plane touches down in a field and rolls to a stop. People gather around it and then carry dozens of blocky parcels to a nearby pickup truck. The parcels turned out to be more than 400 kilos of cocaine.