Authorities subsequently investigated hundreds of deaths, exhuming bodies of former patients.
In all Hoegel was tried in Oldenburg on 100 counts of murder, but the court found him not guilty on 15 counts for lack of evidence.
Pleas are not entered in the German system and during the seven-month trial, Hoegel admitted to 43 of the killings, disputed five and said he couldn't remember the other 52.
Hoegel testified that he had a "protected" childhood, free of violence. He said his grandmother and his father, who were both nurses, had been his role models for going into the profession.
"Now I sit here fully convinced that I want to give every relative an answer," Hoegel said during the trial.
"I am really sorry."In his closing statement to the court on Wednesday, Hoegel reiterated the apology, expressing shame and remorse, and saying he realized how much pain and suffering he had caused with his "terrible deeds."
"To each and every one of you I sincerely apologize for all that I have done," he said.
- AP