A nurse serving a life sentence for two murders has gone on trial for killing another 100 patients at two hospitals in Germany.

Niels Hoegel, 41, is accused of murdering patients at a hospital in the north-western city of Oldenburg between 1999 and 2002 and at another in nearby Delmenhorst from 2003 to 2005. The alleged victims were aged between 34 and 96.

He was convicted in 2015 of two murders and two attempted murders.

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

Niels Hoegel, 41, pictured as a free man told his last trial he enjoyed the feeling of being able to resuscitate patients so he deliberately induced cardiac failure

The Delmenhorst hospital where 62 of the murders are said to have been carried out between 2003 and 2005

The conference centre in Oldenberg being used for the trial is usually reserved for large numbers of defendants but special measures have been made due to the public interest

Hoegel uses a folder to disguise his face in court today

Presiding judge Sebastian Buehrmann opened the proceedings by asking everyone present to stand for a minute of silence for the deceased patients.

'All of their relatives deserve that their memory be honoured,' independently of whether or not Hoegel had anything to do with their deaths, Buehrmann said. 'We will make every effort to seek the truth.'

He promised Hoegel a fair trial and when asked if the charges were accurate, Hoegel replies, 'yes.'

He later told investigators that he also killed patients in Oldenburg.

His method was to inject them with drugs which would bring on cardiac failure and he would then attempt resuscitation.

The prosecution say he wanted to look good in front of colleagues and was also looking for excitement.

Authorities subsequently investigated hundreds of deaths, exhuming the bodies of former patients.

The Oldenburg state court is conducting the trial at a courtroom set up in a conference centre, a venue chosen to accommodate a large number of co-defendants as well as public interest in the proceedings.

If convicted the killer would become one of the worst in Germany's post-war history.

An additional conviction could affect Hoegel'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.

'We have fought for four years for this trial and expect Hoegel to be convicted of another 100 killings,' said Christian Marbach, a representative of the patients' relatives. 'The aim is for Hoegel to stay in custody as long as possible.'

The trial is scheduled to run into May.

The murderer was first caught in 2005 when he injected the wrong drugs into a patent at the Delmenhorst hospital.

Three years later he received a seven year sentence for attempted murder and in 2015 a second trial found him guilty of two murders and two attempted murders.

Police have said that, if local health officials had not hesitated in alerting authorities, Hoegel could have been stopped earlier.

Authorities are pursuing criminal cases against former staff at the two medical facilities.