Thirteen Eritrean detainees have been freed after more than 18 years held without trial in Mai Serwa prison, relatives told the BBC. Among the released is 69-year-old Olympian cyclist and businessman Zeragaber Gebrehiwot, who competed in the 1980 Moscow Olympics. The prisoners were arrested in October 2007 following an assassination attempt on senior security officer Col Simon Gebredingil. Mai Serwa prison is infamous for harsh conditions and holding many political prisoners. The detainees include prominent businessmen Tesfalem Mengsteab, Bekure Mebrahtu, and the Habtemariam brothers, David and Matthews. Six senior police officers and an internal security agent were also released. Relatives said the prisoners were not allowed visits during their detention. Many freed are reportedly sick, which could explain why they were released now. The Eritrean government has not commented on the releases. Human rights groups and the UN accuse Eritrea of widespread abuses, including torture, forced disappearances, and imprisoning tens of thousands under dire conditions. Mai Serwa prison includes metal shipping containers where prisoners are held incommunicado. Eritrea, independent since 1993, remains a one-party state under President Isaias Afwerki, who has ruled for 32 years without elections. The country has no free press since 2001 and enforces indefinite military service. Last year, Berhane Abrehe, a former finance minister who criticized the president, died in prison after being detained without trial for six years. The fate of many political detainees remains unknown, raising ongoing human rights concerns.