ISTANBUL—We don’t know what the soldier with the knife did after the camera was stopped.

The video was horrid enough. It shows soldiers in the uniforms of the U.S.-allied People’s Protection Units (YPG) kicking and stomping on two young Arabs captured near Raqqa. One of the detainees is lying prone under a metal chair, which a YPG soldier sits on, its leg braces grinding into the captive’s back.

“Tell me where are the Daesh fighters. Tell me,” says one soldier, using the pejorative Arabic acronym for the Islamic State.

“I swear I don’t know,” responds the captive. “If you kill me I will not tell you because I don’t know.”

The two detainees are dressed in a traditional galabeyas—the robes used by the people of the area—not the shalwar kameez loose shirts and trousers often worn by ISIS militants.

A second soldier is seen stomping on the back of the second captive.

The two soldiers, both carrying grenades, knives, and sub-machineguns, speak Arabic with a Bedouin accent, indicating they were either conscripts or volunteers who joined the Kurdish-led YPG.

The video raises many questions, but there’s no doubt about its authenticity. Kurdish authorities in northern Syria have acknowledged the incident occurred, and the U.S.-led international coalition said it is investigating.

According to Turkish news media that first published the video, it was taken at the end of May in the Mansura district, west of Raqqa.

One of the questions is how the two captives came into the hands of YPG fighters in the first place. The U.S.-led Raqqa operation is being carried out by the Syrian Democratic Forces, a hybrid Kurdish-Arab force led by Kurdish officers and created at the behest of the U.S. military in late 2015. One reason for creating it was to establish some separation between SDF and YPG, which is the Syrian affiliate of the Kurdistan Workers’ Party, listed as a terror group by the U.S., EU, and Turkey.

If the video is any indication, the SDF in fact works hand-in-hand with the YPG. It’s possible that the SDF captured the men and turned them over to the YPG, but the YPG may have been operating on its own. The U.S. military has refused to embed reporters with its forces on the ground during the Raqqa operation, so little is known about the role of the YPG.

In fact little is known about any aspect of the operation, for the U.S. military has refused to comment on allegations of civilian casualties and damage to civilian property, mosques, bakeries, and markets. The SDF appears to have expelled ISIS from many neighborhoods of Raqqa, but the battle is far from over.

In southern Syria, meanwhile, fighting died down briefly on Sunday, the first day of a cease-fire that President Donald Trump and his Russian counterpart, Vladimir Putin, announced with fanfare after talks in Hamburg. But the Syrian government shelled several towns Monday, indicating that the truce was transitory at best.

The torture video emerged June 30 and was posted by the semi-official Turkish Anadolu News Agency. Still photos from the video were published by A Haber, a Turkish news outlet.

The veracity of the video was acknowledged by the “Self-Protection” body of the administrative area where the incident took place, the Jazira canton, just days after it had surfaced, according to the ARA news agency, which reports on the YPG controlled parts of northern Syria and calls itself an independent news agency.

Denouncing the act “in the strongest terms” the self-protection body said the scene depicted in the video was “absolutely unacceptable and contradicts our ethical and humanitarian frameworks and our values.”

“Since they have broken laws and international norms, they will be held accountable for their irresponsible, individual acts,” ARA reported the defense agency saying.

ARA omitted the “Self-Protection” body’s reference to torture of “one of the ISIS mercenaries after arresting him.” It is not clear how the committee reached the judgment that both captives were “ISIS mercenaries” and only one was tortured.

Omar Alloush, the spokesman for the Democratic Union Party or PYD, the civilian wing of the YPG which rules the Kurdish cantons, said violations of international norms “could happen out of revenge” but they are still individual acts, and “the perpetrators will be held responsible if they are known. He also invited “any committee or objective international organization” to come and open an investigation.

In the past, the YPG has rejected the results of outside investigation that show the group has violated the laws of armed conflict, including a major research by Amnesty International in late 2015, which documented the YPG’s mass expulsions of Arabs.

The U.S.-led international coalition that is conducting the campaign against ISIS in Raqqa, and has provided arms, advisers, and air support for the SDF, said it had forwarded “these allegations” to Coalition elements on the ground and to the Staff Judge Advocate, the military’s legal branch, which investigates war crimes.

“The Coalition does not condone any violation of the laws of armed conflict and works hard in training to ensure partnered forces are aware of and understand the requirements of a professional fighting force to abide with these laws,” spokesman Col. Ryan Dillon told The Daily Beast in an email.

The question is how high up the investigation will go. None of the Kurdish statements indicated any plan to investigate the Kurdish chain of command which had permitted—possibly even authorized—the torture to take place.

There’s also a question about the video itself, which appears to have been shot with the agreement of the two YPG soldiers.

In the final frames of the video, the second soldier, who’s farther from the camera, can be seen signaling that the camera should be switched off.

But as the camera is shut down, the first soldier is poised, knife in his right hand. No one has said what happened next.

—with additional reporting by Duygu Guvenc in Ankara