Warning: This article contains graphic details of torture

“We gave our blood and soul to the revolution,” crowds chanted, as they carried Mazen Al-Hamada’s coffin through the streets of Damascus, draped in the green, white and black flag adopted by protesters back in 2011, now ubiquitous in the city since the fall of Bashar Al-Assad.

As the funeral procession moved forward, more and more people joined it. “Mazen is a martyr,” many shouted, some weeping.

If the world knew before this about the extent of the brutality of Assad’s regime against its own people, it was in part because of Mazen, an activist who was an outspoken critic of the regime.

On Sunday, his body was found in the notorious “slaughterhouse”, Seydnaya prison in Damascus. It bore signs of horrific torture.

A doctor who examined it told the BBC he had fractures, burn marks and contusions all over his body, allegations corroborated by Mazen’s family.

“It’s impossible to count the wounds on his body. His face was smashed and his nose was broken,” his sister Lamyaa said.

A protester when the uprising in Syria began in 2011, Mazen Al-Hamada was arrested and tortured. Released in 2013, he was given asylum in the Netherlands. He began to speak openly about what he was subjected to in prison.

In the documentary Syria’s Disappeared by Afshar Films, Mazen describes how he was raped, his genitals clamped, and how his ribs were broken by a guard jumping on his chest over and over again.