Niels Hoegel, 41, killed several patients between 1999 and 2005 at two medical facilities, Oldenburg and Delmenhorst, in northwestern Germany, primarily to dispel his boredom with life.
Niels Hoegel's deadly drugs of choice were ajmaline, lidocaine and calcium chloride - medications that he would administer to send his patients into arrhythmia, or force their blood pressure to crash to dangerously low levels.
Now, Germany is coming to terms with the full scope of one of its most prolific serial killers since World War II - an apparent mass murderer who managed to escape suspicion for more than a decade because his victims were already critically sick in intensive care units.
Niels Hoegel was sentenced to life in prison after being convicted in 2015 of two murders and two attempted murders.
Separate investigations are looking at the clinics in Delmenhorst and Oldenburg and whether superiors there had cause to suspect foul play in the high number of patient deaths. If convicted, it would at most affect Hoegel's possibility of parole - in Germany, people serving life sentences are generally considered for parole after 15 years.
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The new charges he faces include the deaths of 62 patients at the same hospital. Prosecutor Martin Koziolek said that, in three further cases investigators viewed as suspicious, tests didn't produce enough evidence to add them to the charge sheet.
Hoegel used a variety of drugs in his resuscitation attempts, Koziolek said.
"In all cases (Mr Hoegel) at least accepted the death of the patients as a result of the effect of the drugs", German prosecutors said in a statement. Police also interviewed Hoegel six times to try and get more information while building the case.
Speaking past year, Oldenburg police chief Johann Kuehme said that he believes numerous killings could have been prevented had people been willing to speak out. They added that authorities are already pursuing criminal charges against various hospital staff and administrators.