Writing on Twitter, Santos added authorities would elaborate on the circumstances of the killing of Roberto Vargas Gutierrez, alias "Gavilan," who had been sought for a 500 million pesos (USD 170,000) reward.
The Gulf Clan, which accounts for some 70 percent of Colombia's cocaine production, was born from the remnants of an outlawed right-wing paramilitary group which fought rebels during the country's half-century civil conflict.
The paramilitaries were officially disbanded in 2006, but authorities say their members are still making money from drugs and violence.
Colombia is the world's leading coca leaf grower and also the biggest source of cocaine, producing 866 tons in 2016, according to the UN.
Disclaimer: No Business Standard Journalist was involved in creation of this content