Former Marxist FARC rebel commanders in Colombia, headed by their leader Rodrigo Londono, appeared before a tribunal that will try crimes allegedly committed during the country’s five-decade civil war.

Three members of the FARC’s ruling secretariat attended the first hearing on Friday - Londono, known by his war alias Timochenko, Pablo Catatumbo, and Carlos Lozada. A fourth FARC leader, Jesus Santrich, joined via video conference from prison.

The hearing was a “historic event that constitutes a fundamental step in the efforts to put an end to an armed conflict,” said tribunal magistrate Julieta Lemaitre on the livestreamed session.

The Special Jurisdiction for Peace (JEP) tribunal, founded under a 2016 peace deal between the government and Revolutionary Armed Forces of Colombia (FARC), will try cases considered representative of the war’s violence. The cases are based on investigations by authorities and accusations from victims.

The JEP, which is set to run for at least 15 years, aims to heal wounds left by the conflict and allow victims to hear the truth about loved ones as well as receive compensation from the FARC, including stolen land and property.

Some 7,000 FARC fighters demobilized last year and more than 4,600 of them have already submitted testimony for the JEP under the peace deal, negotiated in the Cuban capital Havana.

The rest of the 31 FARC commanders summoned to the hearing did not attend and were represented by their lawyers.

The former rebel leaders are required by the tribunal to provide details on alleged kidnappings and forced disappearances between 1993 and 2012.

Ransom was one of the rebels’ main sources of financing, along with drug trafficking and extortion. The group earned more than $1.25 billion in ransoms from 8,100 kidnappings during those years, according to the attorney general’s office.

Families of victims say they hope the tribunal will bring to light where the remains of some of those who were kidnapped and murdered can be found.

The FARC began as an insurgency in 1964, fighting for better conditions for the rural poor. More than 220,000 people were killed in a conflict that saw rebels battle the army, right-wing paramilitaries and drug traffickers.