Update — Feb. 26, 8:39 a.m. ET: German male nurse Niels H. was sentenced to life in prison on Thursday for killing two patients, Agence France-Presse reported.
A German male nurse who admitted to killing at least 30 patients between 2003 and 2005 apologized to the victims' families in court Thursday.
Identified only as Niels H. due to Germany's strict privacy rules, the man has been on trial in an Oldenburg court since September for the alleged murders of three patients.
Though a court-appointed psychiatrist said earlier this month that Neils H. had admitted to killing at least 30 patients in his care, prosecutors believed the full number could be over 100 people.
According to the expert, Niels H. admitted to injecting seriously ill patients with an overdose of a potentially dangerous medicine so that he could resuscitate them.
In court on Thursday, the former nurse apologized for his actions.
"I am honestly sorry," the 38-year-old said, according to AFP. "Usually the decision to do it was relatively spontaneous."
Niels H. reportedly told police after he was arrested that he killed the patients because "he was bored." Prosecutors also said that he wanted to practice his "excellent" resuscitation skills, Deutsche Welle, a German broadcaster, reported in November.
The death rate nearly doubled during the time Niels H. worked at the clinic, and the deaths of 174 patients during his shift are under investigation.
The former nurse was previously sentenced to seven-and-a-half years in prison in 2008 for the attempted murder of another patient.
Sixty others have survived his attacks, Sky News reported.
Prosecutors have said that Niels H. injected the patients with a medication that should only be used by doctors under strict supervision. The medicine could cause the heart to function irregularly and blood pressure to drop.
If Niels H. succeeded in reviving a patient, he would sometimes try to medicate them again for a second attempt, prosecutors said.
Court spokesman Michael Herrmann told the Associated Press that after delivering his apology, Niels H. told family members who were there as co-plaintiffs that he hoped it would help them heal, although "he'd understand if they couldn't accept that."
A verdict in the trial is expected next week. Prosecutors are seeking a life sentence, the AP reported.
Tasneem Nashrulla is a reporter for BuzzFeed News and is based in New York.
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Jason Wells is a news editor for BuzzFeed News and is based in Los Angeles.
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