Niels Hoegel, 41, was convicted in 2015 of two murders and four counts of attempted murder or causing bodily harm on intensive-care patients at the Delmenhorst hospital near the northern city of Bremen.
But exhumations and analyses since then have uncovered evidence of scores of other victims, with police saying in August that Hoegel had murdered at least 90 other patients.
On Thursday, police and prosecutors confirmed an additional 16 deaths, bringing the total number of deaths to at least 106 patients at the two hospitals where Hoegel worked between 1999 and 2005.
They said they expected to bring the new charges against Hoegel early next year.
Hoegel has admitted to injecting patients with drugs 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 earlier testified that at times he acted out of "boredom", feeling euphoric when he managed to bring a patient back to life and devastated when he failed.
The death toll "is unique in the history of the German republic," the chief police investigator in the case, Arne Schmidt, said in August, adding that Hoegel killed "without a discernible pattern" and preyed especially on those in critical condition.
Toxicology studies are continuing for five other cases, and exhumations of three former patients are planned in Turkey.
Eyewitness? Submit your stories now via social or:
Email: eyewitness@pulse.ng
