Members of an American-backed rebel group in Syria beheaded a young child in a grisly execution video.

The footage surfaced early Tuesday of members of Harakat Nour al-Din al-Zenki and a captured child in Handarat, near Aleppo. The young boy, who appears to be prepubescent, is then executed on the back of a pickup truck.

The gruesome videotaped murder of a child drew outrage on social media and the promise of an inquiry from the group’s leadership, which has previously received U.S.-made weapons and American funding. The group no longer gets such backing. But it’s also renewed questions about which rebels the American government has supported in Syria’s ongoing civil war.

“Even if they no longer get U.S. aid, it still shows the moral pitfalls of what we’re trying to do in Syria,” Daveed Gartenstein-Ross, a terrorism expert and senior fellow with the Foundation for Defense of Democracies, told The Daily Beast.

There are two clips from the unsavory events. One shows five militants surrounding the boy. In the second, one of them stands over him on the truck and cuts the boy’s head off with a dull knife, raising it over his head.

Details conflict about which groups, exactly, comprise the “moderate” Syrian rebels funded by the U.S.-led coalition, but critics have long warned that fluid dynamics and shifting allegiances on the ground make it difficult to predict which groups will be aligned with U.S. interests.

"We have seen the reports, and we understand that al-Zenki has identified some of its own members as being responsible for this appalling act. We have also seen a statement issued by al-Zenki that it arrested those allegedly responsible," State Department spokesperson John Kirby told The Daily Beast. "We strongly condemn this type of barbaric action, no matter what group is responsible. We encourage al-Zenki to investigate the incident and expect all parties to comply with their obligations under the law of armed conflict."

"Regardless of who may be culpable, we strongly condemn what appears to be ‎the brutal murder of a minor," Kirby added.

Yet the Zenki movement was on the white list as recently as December 2014. A McClatchy report on the U.S.’s decision to stop payment and suspend delivery of weapons to rebel factions noted that the crackdown would not affect the Zenki movement and Harakat Hazm in Aleppo. As many as 1,000 Zenki fighters were on the CIA payroll, according to the article.

A field commander for one of the rebel factions told McClatchy at the time that fighters were paid $150 a month, and that the aid cutoff was in response to gains by the Nusra Front, al Qaeda’s affiliate in Syria. The Islamic extremists of Nusra reportedly seized American weapons from the U.S.-backed groups.

But Thomas Joscelyn, a senior fellow at the Foundation for Defense of Democracies and editor of The Long War Journal, told The Daily Beast that the Zenki movement wasn’t exactly an enemy of al Qaeda’s. Zenki has a long history with the Nusra Front , Joscelyn added—one that has been whitewashed by advocates of funding a moderate opposition.

“Ideologically, it’s definitely hard-line Islamist at a minimum,” he said.

Joscelyn traced numerous interactions between Nusra and the Zenki movement, including one where the latter attacked Nusra on Twitter in English after a confrontation at a checkpoint. But Nusra fired back, demanding they go to a Sharia court and make up, Joscelyn said.

The Zenki movement agreed to all terms and “issued a glowing statement” about cooperation with Nusra, Joscelyn said.

In another instance, Zenki leader Toufic Shehab al-Dine commended Nusra for decimating another U.S.-backed group.

“He basically said, they are corrupt, they deserve to be dismantled,” Joscelyn said.

Yet the Zenki movement used American TOW missiles well into 2015, supplied by an allied forces center that’s reportedly staffed with CIA officials.

It was only in September 2015 that a military commander for the group told Voice of America that they were out of the weapons.

The group also received significant funding from Saudi Arabia, Foreign Policy reported.

An Amnesty International report about human-rights abuses found that Zenka was responsible for torture and forced confessions in Aleppo, where it is based. One media activist who reports on government abuses told Amnesty International that he could hear the sounds of people being tortured while being held by the brigade, though he couldn’t see it happening because of a blindfold. Others said they had received threats for being critical of the movement on Facebook.

More troubling are allegations in the report that the Zenki movement kidnapped Syrian Orthodox bishops on a humanitarian mission and handed them over the the Nusra Front. Yet other activists said they had been tortured by the movement into signing false confessions.

The report notes that the Zenki movement was apparently one of the recipients of aid from MOM, the northern operation command run by the United States and allies. The movement “stopped being funded by it in September 2015 after it joined forces with the Aleppo City Battalion and the al-Zaher Bibers Movement, which was accused of kidnapping two Italian humanitarian workers,” according to the Amnesty report.

Still, the group’s leadership issued a statement condemning the beheading. It said it formed a committee to investigate how such a crime could have happened. Such public executions by rebel groups could bolster embattled Syrian President Bashar al-Assad, who has sought to make all rebel groups out to be bloodthirsty radicals.

But even jihadist groups, Joscelyn said, depend on keeping the goodwill of the areas they pass through, and such actions are beyond the pale.

“What are they gonna do? Say we’re all for beheading children?” he said. “Only the Islamic State would say that.”

—with additional reporting by Shane Harris