A German nurse who used lethal drugs on patients out of boredom has been held responsible for the death of 106 people, a figure which could rise as more bodies are exhumed and studied.

Investigators on Thursday said 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 in Germany.

But recent exhumations and medical analyses have since uncovered evidence of scores of other victims, with the police claiming Hoegel had murdered more than 90 other patients.

The police and investigators also confirmed an additional 16 deaths attributed to the nurse who worked at two hospitals between 1999 and 2005 and who could be facing new charges early next year.

Hoegel had admitted to injecting patients with drugs that can either cause heart failure or circulatory collapse so he could then try to revive them and when successful, could be hailed as a genius by his colleagues.

He also testified that at times, he acted out of boredom, feeling euphoric when he managed to bring a patient back to life and claimed to be devastated on occasions when he failed.