Efraim Zuroff is hoping Aribert Heim will be found in the next few weeks.
Former SS doctor Aribert Heim is still likely to be alive in Chile, a director of the Simon Wiesenthal Centre has said at the end of a five-day mission.
Efraim Zuroff said he was convinced people knowing the whereabouts of the 94-year-old Nazi could be found.
"A person this age cannot live on his own," said Mr Zuroff.
Heim tortured and killed prisoners in Mauthausen concentration camp in World War II, but fled Germany in 1962 before authorities were able to arrest him.
He performed operations and amputations without anaesthetic, and injected victims straight into the heart with petrol, water or poison.
Speaking in Bariloche, southern Argentina, Mr Zuroff said: "There is no evidence that he is dead, but, to the contrary, there are numerous leads that he could be alive."
Heim is accused of killing Jews using exceptionally cruel methods
He said the key to finding Heim was the fact that his daughter, Waltraud Diharce, lived in the Chilean town of Puerto Montt.
"From there he travelled to Bariloche 50 times in one year," said Mr Zuroff.
He also noted no-one had claimed any of the investments or the multi-million dollar bank account in Heim's name - something that would require proof of Heim's death.
Mr Zuroff said that the groundwork had been laid for Heim's capture "in the next few weeks - or at the most, months".
A reward of $495,000 is being offered by the Simon Wiesenthal Centre and the German and Austrian governments.
Mr Zuroff, who heads the centre's office in Jerusalem, said he had been favourably surprised by how much the Argentine government had been supporting the investigation.