Hoegel’s former employers may be held accountable at least in part for the deaths.
"If the people responsible at the time, particularly at the Oldenburg clinic but also later in Delmenhorst, hadn't hesitated to alert authorities - for example police, prosecutors," he could have been stopped earlier, Johann Kuehme, Oldenburg's police chief, told the AP.
Officials are pursuing criminal charges against former staff members of both clinics.
Hoegel admitted during his trial that he caused cardiac crises in approximately 90 patients so could resuscitate them. He said he liked the feeling of bringing them back.
If Hoegel is tried and convicted on any additional charges, it won't affect his life sentences since the German court system doesn't allow for consecutive sentence, the AP reported.