Niels Hoegel, 41, has already spent nearly a decade in jail on a life term for other patient deaths. Detectives say Hoegel administered fatal doses of medication to the people at two hospitals in the north of the country, the BBC reported.
When asked by the judge in court if the charges against him were true, Hoegel confessed to "more or less" all of them. The admission made him one of Germany's worst post-war serial killers.
According to prosecutors, his motive was to impress colleagues by resuscitating the very patients he had attacked.
Hoegel is said to have killed 36 patients in Oldenburg and 64 in Delmenhorst between 1999 and 2005.
The current trial was expected to last till May.
Investigators say that he may have killed even more. "I hope he will be found guilty on each count so that the loved ones can finally find some closure," said Petra Klein, who runs a victims' support group.
Relatives of his alleged victims packed the court.
Hoegel was first caught in 2005 injecting unprescribed medication into a patient in Delmenhorst. In 2008, he was jailed for seven years for attempted murder.
In 2014-15, a second trial found him guilty of two murders and two attempted murders and he was given the maximum sentence.
Hoegel said he was "honestly sorry" and hoped the families would find peace. He said the decisions to carry out his crimes had been "relatively spontaneous".
However, during the trial he confessed to a psychiatrist that he had killed up to 30 people.
Investigators then widened the investigation, exhuming 130 former patients and looking for evidence of medication that could have triggered cardiac arrest. They also pored over records in the hospitals he worked at.
Investigators said the case was "unprecedented in Germany to our knowledge".
Records at the Oldenburg hospital showed rates of deaths and resuscitations had more than doubled when Hoegel was on shift, the German media reported.
(This story has not been edited by Social News XYZ staff and is auto-generated from a syndicated feed.)
