Colombia created a "truth commission" on Monday to help it heal after decades of war under a recent peace deal with the leftist FARC rebels.
President Juan Manuel Santos also signed into law a decree establishing a special unit to search for people still missing in the country's 53-year conflict.
"Today we are signing the legal decrees" to set up the Truth Clarification Commission and the Special Unit for Seeking People Reported Missing, he said in a speech.
The two new bodies are part of a set of special post-conflict institutions to be set up under the peace deal with the Revolutionary Armed Forces of Colombia (FARC).
Special courts are also due to be inaugurated under the accord to try atrocities committed during the conflict.
The heads of the new institutions will be appointed by judicial authorities and foreign delegates including UN officials.
Santos won a Nobel Prize last year for leading the peace effort, which his opponents have fiercely resisted.
Voters narrowly rejected the peace deal in a referendum in October. Critics said it was too soft on FARC members, some of whom would receive amnesties.
But Santos and FARC leaders redrafted the deal before the president successfully pushed it through Congress in March.
Santos said the new post-conflict bodies offer "a guarantee for all those thousands of victims who have spent years and decades waiting for answers."
The Colombian conflict drew in various rebel and paramilitary groups and gangs as well as state forces.
It has killed 260,000 people, displaced nearly seven million and left 60,000 missing, according to official estimates.
Santos has also launched peace talks with the country's last active rebel group, the smaller leftist National Liberation Army (ELN).