Members of former far-right paramilitary groups in Colombia are responsible for about 25,000 murders in recent decades, a report says.

Around 3,700 militants took part in the violence over a period of 20 years. The perpetrators were offered an amnesty program between 2003 and 2006 that guaranteed them milder sentences of up to eight years if they confessed to their crimes, a report by the Attorney General’s Office in Bogota said on Wednesday.

Members of the disbanded United Self-Defense Forces of Colombia (AUC) also admitted responsibility for the disappearance of 2,251 others and the kidnapping of 831 people. In total, authorities were able to find 2,100 graves with the remains of 2,562 people, the report added.

Former AUC members also told judiciary officials of numerous acts of collaboration with politicians, police and the military.

Efforts by Colombian President Alvaro Uribe led to the disarmament of some 31,000 paramilitaries between 2003 and 2006.

Some 247,000 citizens have filed claims as victims of the paramilitaries.