A Nazi officer who was responsible for the deaths of over 128,000 Jews probably died in Syria four years ago, a leading Nazi hunter has revealed.

Former SS Captain Alois Brunner had been advising the Assad regime on torture techniques and was 98 when he died, the Sunday Express reported. Brunner, long one of the world’s most-wanted war criminals and a chief lieutenant of holocaust architect Adolf Eichmann, reportedly fled to Syria in the 1950s and subsequently survived two assassination attempts by Israeli spy agency Mossad.

Dr. Efraim Zuroff, director of the Israel branch of a human rights foundation called The Simon Weisenthal Centre and a leading Nazi hunter, first broke the news of Brunner’s death and said the confirmation came from a former German secret agent who served in the Middle East. The Centre has taken Brunner’s name off its list of wanted Nazis, but Zuroff said they have been unable to confirm his demise forensically due to the Syrian civil war.

“Given his age it would not be surprising and the information came from someone who we consider reliable,” Zuroff said.

Brunner sent thousands of Jews to concentration camps before fleeing the country after the end of World War II, working as a weapons dealer in Egypt and then moving to Syria under the pseudonym Dr. Georg Fischer.

“He was a notorious anti-Semite, sadist, fanatic Nazi,” Zuroff told the New York Times. “The only known interview we have with him was to a German newsmagazine in 1985, in which he was asked if he had any regrets, and he said, ‘My only regret is I didn’t murder more Jews.’”

Write to Rishi Iyengar at rishi.iyengar@timeasia.com.