The former police chief of Guatemala has been arrested in Geneva on Friday for murders committed between 2004 and 2007.
Erwin Sperisen will be questioned over eight murders in prisons in Guatemala.
"He was head of the national police force during two campaigns to execute detainees and we will be looking into those murders," prosecutor Olivier Jornot told Reuters.
Sperisen resigned in 2007 after concerns were raised over involvement of officials in prison murders.
Philip Grant of TRIAL, an NGO campaigning for prosecution of war criminals abroad, welcomed the move.
"NGOs wish that a trial can rapidly take place so that the truth will finally be unveiled and the wall of impunity in Guatemala torn apart," he said in a statement on Friday.