Documentaries about the Syrian civil war are becoming increasingly plentiful, but Matthew Heineman’s “City of Ghosts” stands out for its focus on Raqqa, the city that has been named the capital of the so-called Islamic caliphate proclaimed by ISIS, and the efforts of some of its citizens to reveal what is happening there to the rest of the world. It’s a powerful, remarkable profile of courage under fire, and also a reminder—at a time when a full-fledged assault on Raqqa is being prepared—that the civilian population there represent not terrorist enemies but a brutally oppressed citizenry who should not be thought of as mere collateral damage.

Heineman, who in “Cartel Land” sketched the efforts of Autodefensas, a Mexican self-defense group that fought a drug cartel the government had failed to confront, here focuses on members of the on-line reporting collective called “Raqqa is Being Slaughtered Silently.” Opening with footage of the group’s being awarded one of the International Press Freedom Awards by David Remnick at the 2015 ceremony of the Committee to Protect Journalists, the film describes the creation of what became RBSS by young residents who began recording opposition to the Assad regime in northern Syria beginning in 2012. In 2014, however, ISIS effectively took over the city, and many of them were forced to flee as the militants imposed strict rule over the area. RBSS consists of refugees who left Raqqa for Turkey (or, in some cases, Europe) and now collect, and rebroadcast, clandestinely-shot footage of ISIS atrocities from inside the city taken by a small cadre of underground “reporters.”

The fact that those involved in the group, both in Raqqa and outside it, are putting their lives on the line is made abundantly clear by accounts of assassinations of its members (including a professor who served as their operational mentor). The sheer cruelty of the terrorists is further demonstrated by the videos they circulate of executions—of those whom they consider opponents, including family members of those identified as belonging to RBSS. As the on-air civilian journalists observe, ISIS has grown exceptionally canny in marketing itself with videos that mimic Hollywood tropes, presenting themselves in a heroic light designed not only to suggest their invincibility but to attract new recruits to their banner. All the more reason, they argue, that what they’re doing to their native city has to be shown to the public.

Most of the footage in Heineman’s film is devoted to the refugees working to relay their informants’ dispatches to the wider world, moving from apartment to apartment in Turkey to avoid detection as ISIS mounts an all-out offensive again them, killing their families and friends and issuing direct threats to them in various ways. Eventually most of the RBSS staff must leave Turkey for Germany, where they are transported to what is hoped will be safe residences and even afforded an offer of police protection. They react to their new surroundings with a mixture of amazement and trepidation—a couple is surprised by the liberal atmosphere of Berlin, but the husband hates the cold weather. The reception, moreover, is not universally welcoming: they watch in dismay as a demonstration by rightists demands the deportation of immigrants as job-stealers and possible terrorists. A dark note of irony is also struck near the close when chain-smoking Mohammad, who has become the group’s public face, is watched shaking at the thought of what his future might be as the camera focuses on his pack of cigarettes bearing the warning that they can kill.

Yet the film also carries a hopeful note at the close. Although Mohammad sadly observes that either RBSS will eventually be victorious or ISIS will kill them all, the documentary ends with one of the refugees visiting his newborn son in the hospital, and the suggestion that perhaps the child will be able to go home one day.