Niels Hoegel was convicted in 2015 of two murders and two attempted murders at a clinic in the north western town of Delmenhorst.
A fresh investigation now suggests that he killed at least 84 people.
The true toll is likely to be even higher, said police.
Authorities exhumed hundreds of bodies of Hoegel’s former patients in Delmenhorst and nearby Oldenburg.
They have now unearthed evidence of 84 killings in addition to the ones for which the nurse was convicted.
Police said there are likely to be many other victims among patients who were cremated, meaning that evidence could not be gathered from their remains.
“Eighty-four killings … leave us speechless,” said Oldenburg police chief Johann Kuehme.
“And as if all that were not enough, we must realise that thereal dimension of the killings by Niels H is likely many times worse.”
Mr Kuehme said many of the deaths could have been prevented “if the people responsible at the time… had not hesitated to alert authorities, for example police, prosecutors.”
Authorities are pursuing criminal cases against former staff at the two clinics.
Article Appeared @http://www.itv.com/news/2017-08-28/killer-nurse-may-have-murdered-at-least-86-people-in-germany/