Niels Hoegel, 40, was jailed in February 2015 for two murders and several attempted murders of intensive-care patients at the Delmenhorst hospital near the northern city of Bremen.
Police said on Monday that investigators exhuming and analyzing more bodies had since found evidence of scores of additional murders.
The death toll is unique in the history of the German republic, said chief police investigator Arne Schmidt, adding that Hoegel killed randomly and preyed especially on those in critical condition.
There was evidence for at least 90 murders, and at least as many (suspected) cases again that can no longer be proven, he told a press conference, declaring himself speechless at the outcome.
Hoegel has admitted to injecting patients with a drug that can cause heart failure or circulatory collapse so he could then try to revive them and, when successful, shine as a saviour before his medical peers.
He said he felt euphoric when he managed to bring a patient back to life, and devastated when he failed.
After the revelations of the nurses murderous obsession, police and prosecutors launched a special forensic commission dubbed Kardio (Car...