"I am honestly sorry," the 38-year-old said at his trial, where he so far faces three murder charges, adding that he had usually acted on impulse when he injected patients with lethal drug doses.
"Usually the decision to do it was relatively spontaneous," the defendant, who was identified only as Niels H under Germany's strict court reporting rules, said in his first comments to the court.
He said he knew his actions could not be excused and that he hoped that if he is convicted, the verdict would help the victims' loved ones find peace, national news agency DPA reported.
The ex-nurse went on trial in Oldenburg in northern Germany in September, accused of the murders of three patients and attempted murders of two others, using a heart medication that lowers blood pressure.
A psychiatric expert last month told the trial that the man had admitted to those crimes and that he also claimed to have over-medicated another 90 patients, 30 of whom died.
The court heard his motive was to spark medical emergencies so that he could then demonstrate his resuscitation skills, but that he also acted out of boredom.
The defendant told the court Thursday he was indeed seeking thrills, saying: "There was a tension there, and an expectation of what would happen next."
He said he felt great when he managed to resuscitate a patient, and devastated when he failed.
Each time a patient died, he vowed to never play his lethal game again, but this determination would then slowly fade, he said.
The deaths occurred at Delmenhorst clinic,  near Oldenburg, where the accused worked in the intensive care unit between 2003 and 2005.
The ex-nurse denied having killed anyone at his previous jobs in other clinics, at an elderly home and for emergency medical services.

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