Police in the Colombian city of Medellin have arrested the brother of former president Alvaro Uribe on charges of murder and conspiracy.
Santiago Uribe has been accused of setting up a paramilitary group known as the Twelve Apostles in the 1990s.
It has been linked to the disappearances of dozens of left-wing rebels, drug addicts and criminals in the Antioquia region.
He denies any involvement with the notorious death squad.
The main witness in the case is a former police officer, Major Juan Carlos Meneses, who said that many of the crimes committed by the death squad were planned in the Uribe family’s farm.
Uniformed paramilitaries began training at the La Carolina ranch, in the town of Yarumal, in 1994, said Maj Meneses.
‘Peace with impunity’
Local police were paid to turn a blind eye to the activities of the death squad in the area, he added.
Alvaro Uribe became governor of Antioquia province around that time.
He went on to serve two terms as president (2002-2010) and is now a senator in opposition to President Juan Manuel Santos.
Mr Meneses says he has no evidence connecting the former president to the paramilitary group.
Alvaro Uribe has been very vocal in his criticism of the peace negotiations Mr Santos has been holding with the Farc since November 2012.
“Peace with impunity is unsustainable, it is a bad precedent, a bad example,” he told journalists in Miami in January.
The two sides are expected to sign a peace accord later this month.
Supporters of the former president have accused the government of inflicting political persecution on the opposition.
“The infamous detention of the brother of former President Alvaro Uribe darkens the atmosphere, restricts civil liberties and leaves the opposition without guarantees,” said Senator Paloma Valencia.
Santiago Uribe, a cattle rancher, has not pursued a political career.