Santos spoke at the rebuilt Palace of Justice yesterday during a ceremony to mark the 30th anniversary of the deadly siege, one of the darkest chapters in Colombia's recent history.
He was acting in accordance with a ruling last year by the Inter-American Court of Human Rights condemning the state for the disappearance of 12 people, most of them cafeteria workers, who were taken alive from the building during the 48-hour standoff.
"Stop the gunfire," Santos said. "Stop the gunfire in Colombia forever."
Even in a country long accustomed to political violence including assassinations, civilian massacres and the extermination of thousands of leftist activists, the attack on the court by the now-defunct M-19 rebel movement and the government's heavy-handed response stand out because the events occurred in the very heart of Colombian democracy.
Santos' apology comes after a string of advances in the investigation of the siege, in which 11 Supreme Court justices were among the dead. Last month authorities located in a government warehouse and a potter's cemetery in Bogota the remains of three people who were escorted alive from the court and later disappeared in circumstances that remain murky.
The breakthrough was prompted in part by Santos' three-year-drive to sign a peace agreement with another insurgency, the Revolutionary Armed Forces of Colombia, or FARC. As a deal to halt a half-century of fighting nears, emboldened victims and other witnesses have gradually begun to reveal old secrets about state security forces' role in abuses.