Last year the South African police shot and killed 34 miners after a strike and unrest at a platinum mine in the town of Marikana. The police have long argued that they were acting in self-defense. But footage shown by Britain’s Channel 4 News this week seems to show a more complex series of events.

The footage, apparently taken by a police officer on a mobile phone, was submitted to a commission of inquiry that is investigating the events, Channel 4 News reported. It centers on events in and around a cluster of rocks that has become known to some, using an Afrikaans word for the cluster, as “the killing koppie.”

My colleague Bill Keller visited the cluster recently, while reporting an article for The New York Times Magazine:

I rode up to Marikana with Greg Marinovich, my go-to photographer and guide when I was based in Johannesburg 20 years ago, who spent many weeks documenting the massacre. If you walk the scene, even months later, and note the bits of yellow paint peeling off the reddish rocks where forensic teams marked the fallen, it makes you wonder whether some of the strikers may have been hunted down and killed in retreat. The markings show a scattering of bodies well beyond the sightlines of the initial confrontation; one body lay wedged in the gap between two boulders. “How do you shoot someone in that space?” Greg asked. “Maybe from overhead? Or maybe he crawled in there and bled out. But it looks like an execution at close range.”

The footage lends weight to that idea. It shows police officers walking and shooting far from the initial clash, and the television cameras there, near the rocks of the koppie. At one point an officer is heard over the radio imploring a colleague not to shoot someone. Gunfire can be heard, and the shaky camera then shows a motionless man lying sprawled on the scrub grass. “I shot him at least 10 times,” an officer is heard to say.

The position of spent ammunition, James Nichol, a lawyer for some of the survivors of the killings, told Channel 4 News, could indicate “that police officers were standing on a rock and firing down into a gulley where men were defenseless.”

The headline in the South African newspaper The Mail and Guardian is unambiguous: “Police Shot Marikana Miners Unprovoked, Video Shows.” The police will most likely use the footage, an expert told the newspaper, to support the position “that there wasn’t the mass killing that they are being accused of carrying out.”

An independent investigator, David Bruce, disagreed. “I’m beginning to think that there is more of a possibility that this was a deliberate operation, rather than something carried out in the heat of the moment,” he said.

In a separate Channel 4 News report, survivors of the killing accused police officers of harassing them as they wait to give evidence.