In June of this year, Hamood Almossa received a Facebook chat ultimatum: Give me the names and location of three of your colleagues or we'll kill your father.

Almossa, 22, had planned to become a lawyer, but when the Syrian turmoil began in 2011 he started documenting human rights violations by the Assad regime. Then ISIS invaded his home town of Raqqa in June last year, and Almossa chose to fight the intrusion with a weapon he knows hurts them the most: Truth.

Almossa reports on ISIS activity as part of an underground citizen journalism group called Raqqa Is Being Slaughtered Silently (RBSS), which won the 2015 CPJ international Press Freedom Award for its work.

RBSS works covertly from within the ISIS stronghold of Raqqa and other ISIS-occupied areas in Syria, circulating news reports through its website and social media.

When ISIS invaded his home town of Raqqa in June 2014, Hamood Almossa chose to fight the intrusion with a weapon he knows hurts them the most: The truth. Almossa, now living in Turkey, reports on the war as part of an underground citizen journalists group called Al-Raqqa Is Being Slaughtered Silently (RBSS). (CBC) Almossa, a Syrian media activist who had been criticizing ISIS publicly, fled to Turkey after ISIS invaded Raqqa. He continued his media war against ISIS with the RBSS from Turkey, but his father Mohammed stayed behind.

In retaliation for Almossa's work, ISIS imprisoned his father in April, along with two other men whom ISIS claimed were Almossa's colleagues. ISIS accused the men of coordinating with Almossa and filming events in Raqqa for him.

Almossa said an ISIS communication officer named Abu Qutada contacted him on Facebook asking for the names of three more undercover reporters in exchange for his father's freedom, but he "promptly declined" the request.

This screenshot was taken from a graphic ISIS video, showing Hamood Almossa's father Mohammed just before he was executed. Soon after, in July this year, Mohammed and the two other men were killed. A graphic video of the execution was released by ISIS.

"I am not sad that my dad was murdered by ISIS," Almossa told CBC News during a Facebook chat, in a detached, matter-of-fact fashion. "Do you know how many fathers were killed by ISIS and the Syrian regime recently?

"My father is just a single number among hundreds of civilian casualties … my heart had already died," he said, vowing to continue the journalistic work that drives ISIS crazy.

Rebellious students

RBSS was started by six university students in Raqqa who were expelled from their homes by ISIS and threatened with death because they refused to accept its rule of their city.

Raqqa is Being Slaughtered Silently, whose logo is pictured here, has reporters in Turkey and Syria. (RBSS)

ISIS has the benefit of better cameras, unlimited time and liberty of movement, but Mohammed said his group's visuals have successfully challenged ISIS propaganda. RBSS reporters' videos — clips often shot quickly and secretly with shaky hands — are a more credible news source than ISIS for the people both outside and within Raqqa, he said.

"When we started, we wanted to tell Raqqa people that ISIS was lying to you," Abu Mohammed told CBC via Skype from Germany. He fled there recently from Turkey, where he feared ISIS sleeper agents were looking for him.

An RBSS co-founder who goes by the pseudonym Abu Mohammed, pictured here after he relocated to Germany to avoid militant agents, said he thinks ISIS has not been affected by the coalition airstrikes as much as it has by this group of madly defiant, upstart reporters. (CBC) "And we wanted to tell Syrians that we could rise up against ISIS just as we did against the Syrian regime."

The third aim, made possible through the RBSS website and social media, was to "tell the world that we were being slaughtered silently. And we achieved all three of our main goals," Mohammed said. "Our media reports raised awareness among teenagers who were excited about the victories of ISIS, and (among) the girls who were lured by the illusion of bravery by ISIS fighters."

Mohammed said the group's English language website has revealed the truth to western Muslims who originally bought into the idea that ISIS was establishing a good Muslim caliphate, and who were willing to travel to support it.

"We are calling for our rights," Abu Mohammed said, "and we will continue as long as the Euphrates river of Al-Raqqa is flowing with our blood."

'We won't be muzzled'

The group has grown to 25, allowing RBSS to provide breaking news, features and investigative reports.

It has reporters in Turkey and Syria. The Syrian reporters can't be introduced to each other in case one of them is arrested, Mohammed said, to keep the rest safe from being exposed.

An RBSS founder and its English spokesperson, who goes by the pseudonym Abu Ibrahim Alraqqawi, still lives inside Raqqa. He told CBC News he could not share a lot of specific information about his work for RBSS, but added that he wakes up each day not knowing whether he'll be able to deliver the group's reports to the world.

An undercover reporter challenges ISIS by taking a photo of the RBSS logo in front of an ISIS building. The card says, “We are remaining and expanding, freedom forever.” (RBSS) ISIS shut down WiFi in Raqqa in July in an attempt to impede those who help dissident groups, and prevent the distribution of photos and videos critical of the Islamic State. Alraqqawi said ISIS is putting more restrictions on the use of media, but he won't stop what he's doing "if it is still possible."

"We won't be muzzled," he said, adding that the group wants to expand its coverage into things such as full-length documentaries.

Asked if ISIS is trying to find him, Alraqqawi laughed and said: "They want to have any information about any member of our campaign."

He added that ISIS knows it is being hurt by the efforts of RBSS reporters.

"Before the RBSS launch, when someone wanted to Google Raqqa they'd find results promoting the Islamic State. Now when you Google Raqqa you get news reports on ISIS violations."