SANTIAGO, July 7 (Reuters) - Nazi hunters arrived in Chile on Monday on the trail of Aribert Heim, nicknamed Dr. Death for killing hundreds of inmates at an Austrian concentration camp during World War Two, who they believe may be lurking in picturesque Patagonia.

Heim, who kept the skull of a man he decapitated as a paperweight, is the most wanted Nazi war criminal still thought to be alive. He would be 94 and his family says he died in 1993.

"We are not here thinking that his capture is imminent, but we have to bolster a campaign that we launched a few months ago," Sergio Widder, of the Simon Wiesenthal Center in Buenos Aires, told Reuters on his arrival in Santiago.

Widder was accompanying Nazi-hunter Efraim Zuroff, who head's the Wiesenthal Center's Jerusalem office. The center is offering a bounty of around $450,000 for Heim as part of a new drive to catch aged Nazi fugitives before they die unpunished.

Heim, an Austrian who killed hundreds of inmates at the Mauthausen concentration camp by injecting gasoline or poison in their hearts, has been on the run for 46 years since evading police in Germany in 1962 prior to a planned prosecution.

A doctor with Adolf Hitler's SS, Heim removed organs from victims without anesthetic.

Holocaust survivors remember him relishing the fear of death in his victims' eyes. After administering lethal injections, he timed death with a stopwatch.

The center believes Heim is likely in Chilean or Argentine Patagonia, the region between the Andes and south Atlantic. Heim's daughter lives in the scenic southern Chilean town of Puerto Montt 657 miles (1,058 km) south of the capital Santiago.

Hundreds of Nazis sought refuge in Latin America after World War Two, many lured to Argentina thanks to the open-door policies of Gen. Juan Domingo Peron, as well as to Chile and Brazil.

Josef Mengele, the "Angel of Death" at Auschwitz, escaped to Argentina and also lived in Paraguay before he died in Brazil in 1979. (Reporting by Simon Gardner; Editing by Patricia Zengerle)

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