A nurse serving a life sentence for murdering two patients in northern Germany is now a suspect in at least 84 other murder cases, police say.
The 40-year-old, named only as Niels H under German reporting rules, was convicted of attempted murder in 2006 and murder in 2015.
His victims received lethal drug doses at units where he worked.
Relatives of patients who died in clinics where he worked had urged police to investigate further.
A commission was set up in 2014 to investigate the scale of his crimes, which could make him Germany's worst post-war killer.
The medication caused heart failure or the collapse of patients' circulatory systems.
Judges said he was motivated by a desire to win approval by resuscitating the patients he had drugged.
During his 2015 trial, he admitted applying the drug to about 90 people at an intensive care clinic in the town of Delmenhorst.
Police say the abnormalities stretch back to 2000 at another clinic in Oldenburg.
They said staff had a meeting there in 2001 to discuss the strange levels of deaths and resuscitations, but did not report the levels to police, and Niels H was able to move to the Delmenhorst clinic.
A special police commission was set up in 2014 to investigate the case.
It has been analysing hundreds of medical records and exhumed 134 bodies to test samples for drug residue.
The investigations have been made more difficult because many patients were cremated.
"The findings continue to breach any imagination," said Oldenburg police chief Johann Kuhme. "It is simply not possible to say how many people were killed."
Mr Kuhme warned the number could still rise further. The new charges are now likely to be filed at the beginning of 2018, he said.
