A doctor appointed by a Chilean court to examine whether former President Augusto Pinochet is fit to be tried has diagnosed him with "moderate dementia".
Gen Pinochet has said he had no knowledge of the killings
Judge Juan Guzman will now decide whether Mr Pinochet can face charges of kidnapping and killing his opponents.
The former military ruler denies any role in Operation Condor, a scheme in which South American dictatorships eliminated their left-wing critics.
The BBC Santiago correspondent says the test results are not definitive.
Two other doctors who examined Mr Pinochet along with the court-appointed doctor came to different conclusions.
A doctor acting for the relatives of victims of Operation Condor said Mr Pinochet was mentally fit enough to face trial.
KEY DATES IN PINOCHET'S LIFE
1973: Leads coup against left-wing President Salvador Allende
1988: Loses plebiscite on rule
1990: Steps down as president
1998: Retires as army commander-in-chief. Arrested in UK at Spain's request
2000: Allowed to return to Chile
2004: Supreme Court strips his legal immunity
However, a doctor acting for Mr Pinochet's defence said his tests showed the former president's health had deteriorated recently and he ought to be spared a trial.
Judge Guzman appointed the three doctors to examine Mr Pinochet so that he could reach a decision on whether to try him.
He said he now plans to meet doctors and the lawyers for both sides before reaching a decision.
A dementia diagnosis helped Mr Pinochet escape prosecution in 2000, while he was detained in London on the orders of Spanish judge Baltasar Garzon.
Judge Garzon wanted to have him extradited and tried for alleged human rights abuses committed during his rule from 1973 to 1990.
An inquiry has concluded more than 3,000 people were killed for political reasons during that period, while more than 30,000 Chileans have testified that they were tortured or detained by the military government.
The former strongman's lawyers have argued that attempts to prosecute their client are a form of victimisation.
However, human rights lawyers say Mr Pinochet is fit to face trial, pointing to a recent television interview in which he appeared capable of defending himself against accusations.