A German nurse on trial suspected of murdering 150 patients in his care told police after he was arrested: 'I got bored.'

Nils. H., 38, is being tried for just three specimen murders by injecting patients with a dangerous medicine.

Some of his alleged victims were on the mend, others seriously ill. Prosecutors in the district court of Oldenburg said he was bored and wanted to practice his 'excellent' resuscitation skills.

Nils. H. (pictured left concealing his face as he arrives for his trial) is being tried for just three specimen murders by injecting patients with a dangerous medicine

According to the prosecution, if the first attempt at resuscitation was a success, H. would sometimes make a second attempt.

H., whose full name is withheld under German privacy laws, used Gilurytmal, a medication which should only be used by doctors under strict supervision, it was said.

Side effects include an irregular heartbeat, a drop in blood pressure and uncoordinated functioning of the heart muscle.

Though H. is facing charges in three murders and two attempted murders, the state prosecutor has said he could be involved in more than 150 deaths.

In cooperation with the police, the state prosecutor is currently investigating the deaths of 174 patients who died during H.'s shifts from 2003 to 2005 at a clinic in Delmenhorst, near Bremen.

Prosecutors in the district court of Oldenburg said Nils. H. (pictured) was bored and wanted to practice his 'excellent' resuscitation skills

The investigators will also look into deaths at H.'s previous jobs in Oldenburg and Wilhelmshaven and dozens of bodies will have to be exhumed.

In 2008, Nils H. was previously sentenced to seven-and-a-half years for the attempted murder of another patient.

He gave his patient an overdose of heart medication, though the man narrowly escaped death.

The death rate in the Delmenhorst clinic nearly doubled in the time H. worked there, and use of the heart medication also increased dramatically.

But it took nearly a decade before an investigation was launched, angering relatives of the dead who are demanding information.

Though H. is facing charges in three murders and two attempted murders, the state prosecutor has said he could be involved in more than 150 deaths

A senior doctor who gave evidence in September said H. was a 'passionate medic' who made a good impression on staff at the clinic.

But the doctor added: 'I found it strange that he was always on hand when patients were being resuscitated, often helping younger doctors with intubation - inserting a breathing tube into a patient's airways.'

'No one wants to believe that a colleague would rather kill patients, instead of helping them,' said Erich Joester, a lawyer for the clinic.