Amnesty International has urged the Syrian authorities to reveal the whereabouts of four activists arrested last week near Damascus after the dead body of their friend was returned to his family over the weekend.
The four, who include the brothers Yahya and Ma'an Shurbaji, have not been seen since they were detained in Daraya, a Damascus suburb, on 6 September at the same time as Ghayath Mattar, the dead activist. There are growing fears for their safety.
An Amnesty International report last month listed 88 deaths in custody since April, but seven others, including Ghayath Mattar, have died behind bars in recent weeks, bringing the total to 95.
"It is clear that these human rights activists from Daraya are in grave danger given the very suspicious circumstances surrounding the death of their friend and fellow activist Ghayath Mattar," said Philip Luther, Deputy Director of the Middle East and North Africa Programme at Amnesty International.
"The spiralling total of detainee deaths together with the Syrian authorities' failure to conduct any independent investigations points to a pattern of systematic, government-sanctioned abuse in which every detainee must be considered at serious risk," said Philip Luther.
The official account given to Ghayath Mattar's family by security officials is that he was "shot by armed gangs" although he is known to have been in detention since 6 September and video and other evidence suggests that he was tortured prior to his death. The 26-year-old had helped to lead peaceful protests in Daraya in which demonstrators responded to the security forces' violence by carrying flowers.
Ghayath Mattar and Yahya Shurbaji were arrested by plain-clothes officers on 6 September after Yahya Shurbaji's brother Ma'an called to say he had been injured when security forces raided his home. Sources have told Amnesty International that Ma'an Shurbaji was already in custody at the time, and was forced to make the call to lure his brother in for arrest.
Two other activists from Daraya, Mazen Zyadeh and Mohamed Tayseer Khoulani, were reportedly arrested at the same time as Ma'an Shurbaji. Air Force Intelligence confirmed Ghayath Mattar's arrest on 6 September in a telephone call to his family days before his body was handed over to them.
"Yahya Shurbaji is at particular risk, given his active role in organizing peaceful protests since March. Syrian authorities must immediately reveal the detainees' whereabouts and give them access to lawyers, their families and any needed medical assistance," said Philip Luther.
Fears also continue to grow for six other activists from Daraya whose families have had no access to them since they were arrested in July and August. Like those detained on 6 September, they are believed to be held by Air Force Intelligence, one of several Syrian security agencies and the main one currently operating in Daraya.
According to a family friend, security forces surrounded the cemetery when Ghayath Mattar was buried to try and prevent the family from holding a public funeral, then used live fire against mourners, killing a 17-year-old boy and injuring four others.
Syrian authorities have not publicly said if any charges have been brought against the activists still in detention, but Amnesty International believes that they were detained for their involvement in pro-reform protests.
"If these men are being held solely on the basis of their peaceful human rights activism, we would consider them to be prisoners of conscience and they must be released without delay," said Philip Luther.