A former nurse serving a life sentence for murder went on trial Tuesday on charges that he killed a further 100 patients at two hospitals in Germany.

Niels Hoegel, 41, told a court in the northwestern city of Oldenburg that the charges against him were largely accurate, news agency dpa reported. The trial began with a minute of silence for the patients.

The murder charges stem from Hoegel's time at a hospital in Oldenburg between 1999 and 2002 and at another hospital in nearby Delmenhorst from 2003 to 2005. The alleged victims were aged between 34 and 96.

Hoegel was convicted in 2015 of two murders and two attempted murders. During that trial, he intentionally brought about cardiac crises in some 90 patients in Delmenhorst because he enjoyed the feeling of being able to resuscitate them. He later told investigators that he also killed patients in Oldenburg.

Niels Hoegel hides behind a folder as he arrives in court on Tuesday. Julian Stratenschulte / AFP - Getty Images

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

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

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 honored," 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.

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 last until May.

Police have said that, if local health officials hadn't hesitated in alerting authorities, Hoegel could have been stopped earlier.

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