BUENOS AIRES, July 17 (UPI) -- A world-renowned Nazi hunter said Thursday he was closing in on a former SS physician who lived for decades after the war in either Chile or Argentina.

Efraim Zuroff, a director of the Los Angeles-based Simon Wiesenthal Center, told reporters in the Argentine capital that his investigation turned up at least four people who said they had seen Aribert Heim in the last month and a half, Clarin reported online.

Heim, 94, is charged with killings at the Mauthausen concentration camp in Austria and is thought to have fled Germany for South America is 1962.

The German and Austrian governments along with the Wiesenthal Center are offering a reward of $500,000 for information leading to Heim's arrest and prosecution.