A nurse serving a life sentence for two murders is going on trial on charges that he killed a further 100 patients at two hospitals in Germany.

Niels Högel’s trial is to open on Tuesday (local time) in the north-western city of Oldenburg.

The murder charges against Högel, 41, stem from his time at a hospital in Oldenburg, a city on the North Sea coast, between 1999 and 2002 and at another hospital in the nearby city of Delmenhorst between 2003 and 2005.

But while Högel is on trial for the death of 100 patients, German weekly magazine Der Spiegel has reported that special investigators had identified up to 322 potential victims.

The magazine also reported the prosecution had exhumed 134 bodies – some as far away as Poland and Turkey – to examine for traces of drugs that Högel may have used.

One expert close to the investigation alleged to Der Spiegel that Högel” probably killed between 200 and 300 people”.

However, more than 100 of the former patients were cremated, the report said.

Högel was convicted in 2015 of two murders and two attempted murders at a hospital in Delmenhorst.

During that trial, he said he intentionally brought about cardiac crises in about 90 patients there because he enjoyed the feeling of being able to resuscitate them.

He later told investigators he also killed patients in Oldenburg, sparking subsequent investigations by authorities.

The ABC reported that Oldenburg police chief Johann Kuehme last year said other medical staff in Oldenburg were aware of a large number of resuscitations, and initial indications of possible wrongdoing by Högel in Delmenhorst emerged as far back as April 2003.

Niels Högel (R), guided by his lawyers Ulrike Baumann (C) and Kirsten Huefken (L). Photo: Getty

Mr Kuehme said many of the deaths could have been prevented if health authorities had acted more quickly on their suspicions.

An additional conviction could affect Högel’s possibility of parole, but there are no consecutive sentences in Germany.

In general, people serving life sentences are considered for parole after 15 years.

Such is the huge public interest in the trial, it is being held in a 700-square-metre space in the Weser-Ems-Hallen convention centre in Oldenburg, normally reserved for big music acts. The area will hold about 350 spectators, with 200 spots reserved for the media.

-with agencies