Former SS captain Alois Brunner. Screenshot/https://www.youtube.com/watch?v=3ArgP-AtR2M The world's most wanted Nazi criminal, Adolf Eichmann's second-in-command, died four years ago in Syria at age 98, the Simon Wiesenthal Center said Sunday, citing the testimony of a former German secret service agent deployed in the Middle East.

SS captain Alois Brunner, described by Eichmann as his "best man," was responsible for the deportation of 128,500 Jews to the death camps.

After World War II, in the 1950s, Brunner fled to Syria, where he reportedly served as a government adviser to President Hafez Assad and is thought to have instructed the regime on torture tactics.

He survived two Mossad assassination attempts and went to his grave utterly "unrepentant," according to Nazi hunter Efraim Zuroff.

"We have received information from a former German secret service agent who had served in the Middle East who said that Brunner was dead and buried in Damascus," Zuroff told The Sunday Express on Sunday.

"Given his age it would not be surprising and the information came from someone who we consider reliable."

Because of the ongoing Syrian civil war, the precise location of Brunner's grave remains uncertain.

Brunner managed to flee Germany because of an identity mix-up that saw fellow SS member Anton Brunner prosecuted and hanged for his crimes. In 1954, using a fake Red Cross passport, Brunner traveled to Rome and later Egypt, where he rented a room from a Jewish family. In 1985 he said they were "quite nice people, really."

After arriving in Syria under the pseudonym of Dr. Georg Fischer, Brunner was said to serve as an adviser to Assad on torture methods, though the information has not been confirmed. The Syrian government shielded Brunner from the various extradition orders.

Nazi fled justice for a new ‘job’ as torturer for Syria’s murderous regime http://t.co/bnK7gym3AU If only we could have caught him... — Efraim Zuroff (@EZuroff) November 30, 2014

"He was involved in the harsh treatment of the Jewish community of Syria and was an expert in terror and torture," Zuroff said. "He said himself his one regret was he did not kill more Jews. He was unrepentant."

Brunner was injured in two separate attempts on his life by the Mossad in 1961 and 1980.

"He lived under the false name of Georg Fischer but his presence was no secret. He actually received two letter bombs, apparently from Mossad. He lost three fingers and an eye," Zuroff said.

According to the Simon Wiesenthal Center, Brunner organized the deportations of 47,000 Austrian Jews, 44,000 Greek Jews, 23,500 French Jews, and 14,000 Slovakian Jews to the concentration camps. "The majority were murdered," Zuroff said.

"Among Third Reich criminals still alive, Alois Brunner is undoubtedly the worst. In my eyes, he was the worst ever," Nazi hunter Simon Wiesenthal wrote in his memoirs. "While Adolf Eichmann drew up the general staff plan for the extermination of the Jews, Alois Brunner implemented it."