OLDENBURG, Germany — The former nurse’s crimes were “incomprehensible,” a German judge told the court on Thursday, reaching his arms across the breadth of the bench as if to capture in one gesture what he sensed his words had failed to define — the enormity of murdering 85 patients who had been placed in the care of the nurse but instead had found death.

“Your guilt is so large that one can’t explain it,” the presiding judge, Sebastian Bührmann, told the nurse, Niels Högel, in a courtroom packed with the relatives of the 100 patients whose deaths he was charged with orchestrating. “It is so large, you can’t show it.”

Mr. Högel is believed to be the most prolific serial killer in peacetime Germany, and perhaps the world. His trial on the 85 murders sought to provide a measure of comfort and answers to some of the victims’ families, more than a decade after they died. His conviction on Thursday was the third for the nurse.

[Read our previous coverage: Hundreds of Bodies; One Nurse]

Officials suspect Mr. Högel may have killed as many as 300 patients while working at two clinics in northern Germany between 2000 and 2005. He was accused of administering drug overdoses that caused cardiac arrest so that he could try to revive patients heroically. His colleagues called him “Resuscitation Rambo.”