Sheltered from a Patagonia downpour, Efraim Zuroff sits outside the house of the daughter of the most-wanted Nazi thought to be alive, waiting.

Zuroff, who has tracked down dozens of Nazi fugitives in the past 28 years, travelled to the southern tip of Chile this week to look for what would be the final prize.

Aribert Heim, nicknamed "Dr. Death" for killing hundreds of inmates at Austria's Mauthausen concentration camp, could be the last major Nazi still underground, says Zuroff.

A doctor with Adolf Hitler's SS, Heim became known for gruesome experiments that Zuroff says included removing organs without anaesthesia and injecting gasoline into the heart.

Heim, one of hundreds of World War Two war criminals to seek sanctuary in Latin America, would be 94 years old.

While the former Nazi's family claims Heim died in 1993, Zuroff says there are still unclaimed bank accounts and stocks in his name. The trail heated up after an informant said he saw Heim's son-in-law deliver food to an ostensibly empty place.

Zuroff, who leads the Simon Wiesenthal Centre's search for war criminals, hopes someone from the surrounding community of Puerto Montt, 657 miles (1,058 km) south of the capital Santiago, will go for the half a million dollar reward the centre is offering for Heim's capture as part of its "Operation Last Chance."

"We have to find the weak link," he said. "Maybe someone will be disgruntled and decide that for 315,000 euros it's worth it to turn the tables on someone who's as terrible as Heim."

So far, he's had no luck.

At the modest chalet of Heim's daughter, Waltraud Diharce, and her husband, Ivan, smoke billowed from the chimney and a dog padded around the garden. Through lace curtains, paintings of mountain scenes and model boats were visible. Two cars registered to the couple sat in the driveway.

A housekeeper, opening the door a crack, said they weren't home.

SIX DECADES LATER

Heim has been on the run for 46 years since evading police in Germany in 1962 before prosecution.

Heim famously decapitated one victim and boiled the head to remove the flesh so he could keep it as a paperweight, Zuroff said. He would time death with a stopwatch, and decorated his office with body parts, he said.

Six decades after the war ended, governments are reluctant to prosecute Nazi war criminals, hoping the biological solution - death - will make the problem disappear, he said.

"In most cases it's not even a case of amassing the evidence, the problem is simply getting the governments involved to do the right thing," he said. "The problem really is a political problem, which is the sad part of it."

Austria, Latvia, Estonia and Lithuania are Nazi havens, he said. The more time that passes, the less pressing catching Nazis becomes to the wider world.

"Time is running out," said Zuroff, 59, who vows not to retire until there are no more Nazis left unpunished. "This issue, unlike anti-Semitism, is coming to an end."