Niels Hoegel was convicted of killing two patients, and attempting to kill two others in 2015. He was sentenced to life in prison for his crimes. Now, prosecutors allege Hoegal is behind the murder of 97 other patients over several years.
According to Time, Hoegel admitted to the murders during his original trial, causing police to open investigations of their deaths. He said he "intentionally brought about cardiac crises in about 90 patients in Delmenhorst because he enjoyed the feeling of being able to resuscitate them."
The BBC reports that investigators had to dig through records from years ago, and in some cases had to exhume the bodies of the deceased.
Investigators exhumed 130 former patients, looking for traces of medication that could have shut down their cardiovascular systems. They also pored over records in the hospitals he worked at.
Authorities believe there could be more victims, but they were unable to examine the bodies because they were cremated.
Authorities hope to begin a new trial for the 97 murders sometime this year. Any new convictions will not add to his sentence, as he is already serving life in prison, but it could impact his chance for parole. In Germany, convicts sentenced to life in prison are usually eligible for parole after 15 years behind bars.
Police are also investigating the two clinics where he worked, looking to see if any staff knew about his actions. Records at both clinics indicate an increase in rates of deaths and resuscitations while he was working.