Colombia has ordered the arrest of a right-wing paramilitary leader in connection with the killing of his brother, another paramilitary leader.
Carlos (l) and Vicente Castano were key figures in the AUC
Prosecutors allege Vicente Castano ordered Carlos's killing in 2004. But they have not declared him dead as they have yet to find his remains.
Vicente Castano is also wanted by the US authorities for drugs trafficking.
He is the one of the few paramilitary leaders who has not turned himself as part of a peace deal, or been arrested.
Peace talks between the government and the paramilitaries have so far led to more than 31,000 members of the group giving up their weapons in return for reduced prison terms among other benefits.
It was Carlos Castano, as leader of the umbrella group United Self-Defence Forces of Colombia (AUC), who started negotiations with the government.
Prosecutors allege that other members of the group feared Carlos would give Washington information about drugs trafficking networks.
That, they say, is why his brother may have ordered the killing.
A number of men, including Vicente Castano's security chief, are already in custody in connection with the investigation.
The AUC has its roots in the paramilitary armies built up by drug lords in the 1980s, and says it took up arms in self-defence, in the place of a powerless state.
It is blamed for many massacres and kidnappings in Colombia's long-running civil conflict, which has involved paramilitaries, left-wing rebels and state forces.