The 37-year-old man responded only by saying, “I'm remaining silent” when the accusations were read out on the first day of the trial in Oldenburg, Lower Saxony.
He is accused of injecting five patients with a drug that causes serious heart and circulation problems between 2003 and 2005.
Three patients, a woman aged 61 and two men aged 44 and 78, were definitely killed by the drug, while it could not be determined whether two further patients had died of their illnesses or the effects of the medication.
The nurse acted out of boredom and the desire to show off his resuscitation skills, prosecutor Daniela Schiereck-Bohlmann said, and counted the possible death of the patients an acceptable risk.
According to one senior doctor who gave evidence, the accused was a “passionate medic” who drove ambulances in his spare time and made a good impression on staff at the clinic.
The doctor did remember finding it strange that the nurse was always present when patients were being resuscitated. He was especially skilled at intubation - inserting tubes - often helping younger doctors with the procedure.
“There was no thought to ask about why he was always there,” the doctor said.
The accused has already been convicted once of a similar crime at a 2008 court case and is serving a seven-year prison sentence.
After that conviction, it was found that the rate of usage of the drug involved, Ajmaline, had increased by almost 10 times at the clinic between 2001 and 2005, and the death rate had also increased.
The drug could be ordered and administered by nurses without doctors writing a prescription.
A woman became suspicious when she learned of the case as her mother had died suddenly at the clinic in Delmenhorst, Lower Saxony, where the nurse worked. She brought charges and a new investigation was started.
The trial is expected to last into 2015.