Former Nazi death camp guard John Demjanjuk, sentenced to five years in a German prison last year, has died at the age of 91, police said Saturday.

The Ukrainian-born Demjanjuk had been found guilty of almost 28,000 counts of accessory to murder during the six months he was a guard at the Sobobor death camp in 1943.

The ailing Demjanjuk was sentenced by a Munich court in May 2011 after a trial lasting 18 months. However, he was allowed to go free, having already spent nearly two years in prison on the grounds that he was not a threat and was unlikely to abscond, being stateless.

While there was no direct evidence of his presence or actions at Sobibor in German-occupied Poland, the court said it believed he had served there as a guard, and was therefore automatically implicated in killings carried out there at the time, mainly of Dutch Jews.

He had denied the charges and appealed against his conviction.

Demjanjuk went to live in the United States after the war but in 1986, he stood trial in Jerusalem accused of being "Ivan the Terrible," an infamous Ukrainian guard at another death camp, Treblinka.

Found guilty of all charges and sentenced to death in 1988, he was freed five years later when evidence surfaced proving Israel had got the wrong man.

After evidence emerged that he served as a guard at other Nazi camps, he was stripped of his US citizenship in 2002 for lying about his war record on immigration forms.

After years of legal wrangling, he was deported from the United States to Germany in 2009 to face trial anew.