“They said it was better that we kill ourselves than wait for you to kill us,” he said, looking at the activist crouching beside him. “They were from our own group.”

Throughout the videos, members of the Free Syrian Army professed a commitment to religious pluralism and said the survivors of Aqrab were under their protection. Nevertheless, there were moments when flashes of sectarian animosity shone through. In one video, a rebel fighter could be heard saying to an injured young man, “Get well soon, even if you are in the Alawite sect.”

“Man, so what if I was in the Alawite sect?” the injured young man protests, as medics busily gathered around his bare legs. A second rebel, standing nearby, interjected and stroked his face.

“Bashar does not represent the Alawite sect,” the second fighter reassured the victim. “The Syrian people are one.”

The Syrian Observatory for Human Rights said it believed the massacre victims had died from “gunfire and bombs.” Almost all were members of the Alawite sect.

The observatory also could not confirm the circumstances of their deaths, but said it had identified several similar narratives of the attack. One was that shabiha members had sought cover among civilians in a residential area, using them as shields. Another was that “pro-regime militiamen held Alawite civilians captive.” It also said that explosions had caused many of the deaths.

Syria’s conflict began as an Arab Spring protest movement after four decades of rule by the family of Mr. Assad, and has since transformed into a sectarian conflict. Even so, attacks by Alawite militias on their own civilian populations have so far been unheard-of.

Faiek al-Meer, a longtime antigovernment activist, wrote on Facebook that the Aqrab episode could be seen as a metaphor for the predicament facing the entire Alawite sect. Mr. Assad, he wrote, “will continue to fight to defend his seat and the interests of his clique even if has to use the Alawites as human shields to protect himself.”