The Holocaust, an intensely organized, systematic genocide, resulted in the brutal massacre of millions during World War II -- and remains a horrific, dark time in world history. There is still enormous public outcry for the prosecution of Nazi war criminals -- at least for those who are still alive. We've tracked down the last remaining Nazi war criminals, some on trial, some just suspects.

John Demjanjuk

John Demjanjuk, an 89-year-old retired Ohio autoworker, is the lowest-ranking person to go on trial for World War II Nazi war crimes to date. He is charged with being an accessory to the murders of 27,900 people while serving as a guard at the Sobibor death camp in Nazi-occupied Poland. Throughout the 32-year-long legal battle, Demjanjuk has claimed he was a captured Soviet soldier and held as a Nazi prisoner of war. German prosecutors argue he volunteered to serve in the German SS and was stationed at Sobibor.

Jakiw Palij

Polish-born Jakiw Palij, who migrated to New York City after World War II, was stripped of his American citizenship in July 2009. Federal prosecutors in the United States are accusing him of serving at the Trawniki death camp in Nazi-occupied Poland in 1943, when some 6,000 Jews were killed. He is also charged with serving at nearby secret service training camps. The 80-year-old claims he never went into any concentration camps, nor took part in any killings, but says he was forced to serve as a guard on a troop base under penalty of death.

Helmut Oberlander

Now well into his 80s, Helmut Oberlander has fought to keep his Canadian citizenship since 1995. Captured Nazi documents showed that Oberlander served in a German SS mobile killing unit. His unit was responsible for murdering tens of thousands of Jewish and other civilians in Nazi-occupied Ukraine and former Soviet territories. Oberlander maintains he served only as a translator, never participated in any killings and was threatened with death if he attempted to leave.

Adolf Storms

Former SS sergeant Adolf Storms lived in Germany unnoticed for almost 60 years before an Austrian university student found his name while researching a Holocaust-related massacre. The 90-year-old retiree is now charged with 58 counts of murder for the killings near the Austrian village of Deutsch Schuetzen. Storms is also accused of shooting a Jew who could no longer walk during a forced march in Austria from Deutsch Schuetzen to the village of Hartberg -- a distance of over 35 miles. German courts are still deciding whether there is enough evidence to bring the case to trial.

Charles Zentai

Australian officials approved the extradition of 88-year-old Charles Zentai to Hungary in November 2009 after he was accused of beating a Jewish teenager to death during World War II. Zentai is accused of murdering 18-year-old Peter Balazs in Budapest while serving in the Hungarian army, then allied with Nazi Germany. Zentai's son claims his father wasn't in Hungary at the time of the murder, and his family plans to fight the charges.

Heinrich Boere

Charged with murdering three Dutch civilians in 1944, 88-year-old Heinrich Boere is currently standing trial in Aachen, Germany as a Nazi war criminal. At the end of World War II, the SS officer fled the Netherlands and lived in Germany, where he dodged several convictions. In 1949, a court in Amsterdam convicted and sentenced him to death (it was later commuted to life in prison). An attempt to extradite Boere to the Netherlands failed in 1983, when it was thought he could have German citizenship (Germany didn't extradite its citizens at the time). In 2007, another German court ruled that Boere shouldn't have to serve his Dutch sentence in a German jail. Finally, the Central Office for the Investigation of Nazi Crimes picked up the case in 2009 and succeeded in pushing it to trial.

Josias Kumpf

After admitting he took part in two massacres as a Nazi concentration camp guard, 83-year-old Josias Kumpf was deported to Austria from his home in Wisconsin in March 2009. Kumpf admitted that he participated in Aktion Erntefest -- Operation Harvest Festival -- where 42,000 Jews were killed at three Nazi camps in eastern Poland in two days. He also admitted to being an assassin during the mass shootings at the Trawniki Labor Camp, where some 8,000 people were killed in pits. He died earlier this year, according to one report.