In Oldenburg, a town in northern Germany, began a trial against a nurse accused of killing 100 patients. Detectives say Niels Högel, 41, was injecting fatal doses to his patients at two different hospitals.

Högel is currently serving a life sentence for killing people under his care. This trial, which is expected to last until May, is based on toxicology tests of more than 130 exhumed bodies recently. Högel is accused of killing 36 patients in Oldenburg and 64 in Delmenhorst between 1999 and 2005.

This case is unprecedented in Germany. If found guilty, Högel will be one of Germany's most cruel serial killers after the war. Investigators say they may have killed even more people, but the bodies of potential victims are cremated.

"I hope to be found guilty of each count, and finally, family members of the victims find peace," said Petra Klein, who leads a group for loved ones and victims.

Högel was arrested for the first time in 2005 after being caught by injecting a patient without the doctor's approval. Högel was sentenced to seven years' imprisonment in 2008 for attempted murder. In a second trial he was found guilty of attempted murder and murder at the other five casualties and sentenced to 15 years.

At the moment, Högel told the psychiatrist he had killed at least another 30 people at Delmenhorst. As a result, investigators investigated suspicious deaths in Oldenburg. Authorities say the number of casualties can reach up to 200, but the truth will never be revealed.

Högel followed the same procedure every time. At first, he injected patients into a medication that caused cardiac arrest and then tried unsuccessfully to bring them to life. Investigators say he was motivated by vanity or simply by boredom. Victims were common, from 34 to 96 years old.