“The course of events that took place on June 24 are symbolic of the failure of those responsible for their completely erroneous assessment of actual facts and the tragic results that ensued for the patients,” Mr. Schmidt said, announcing the results of his investigation in 2017.

That investigation came about only after years of pressure by family members, and led to the current trial.

Two former prosecutors from Oldenburg were investigated for failing to sufficiently investigate Mr. Högel in 2005, but neither faced charges. One is now a judge in Oldenburg.

Judge Bührmann opened the current trial with a moment of silence to honor the victims. At times, the proceedings have seemed more like a truth commission than a criminal trial.

“The purpose of this trial is to provide answers for the family members whose loved ones died, to help them to understand how and why,” Judge Bührmann told a witness.

But Mariya Tüter, 47, expects more. Three years ago, the police told her they suspected that her husband, Adnan, might have been murdered by Mr. Högel. Since then, she has struggled with depression and, at times, even to drive to the supermarket.

“Until this happened, I saw doctors as people who did the right thing; they were there to be trusted,” she said. “But in this case, they swept everything under the carpet. I finally want justice to be served.”