The US has extradited a Peruvian ex-army officer, Telmo Hurtado, over the killing 69 villagers during the war against Maoist guerrillas in the 1980s.
Hurtado is accused of commanding a patrol that killed the civilians, who included women and children.
He was included in an amnesty for officers in the 1990s, but lost his immunity from prosecution when Peru's Supreme Court later nullified the law.
He fled to the US, where he was arrested in 2007.
On Friday Hurtado is to appear before a Peruvian court that will decide where he will be held while prosecutors prepare the case, a lawyer for families of the victims told AFP news agency.
He is alleged to have taken part in the "Accomarca Massacre" in August 1985, when army units entered a village and killed dozens of residents.
Hurtado - who was known as the "butcher of the Andes - was originally convicted in 1993, but later included in a blanket amnesty for officers. The amnesty law was nullified in 2002.
Peru's army fought bitterly against Maoist guerrillas belonging to the Shining Path movement in the 1980s and 1990s.
The military has been accused of rights abuses, but few people have been charged.