For years, the father of Frederike, who was killed in 1981, fought for a new murder trial.
The allegations were directed against a man who had been acquitted in 1983 for lack of evidence in the case.
Now the father died shortly before the planned new trial, as a spokeswoman for the Verden district court told the dpa on Monday.
The "Hannoversche Allgemeine Zeitung" (HAZ) first reported on the death of the 79-year-old.
"He cannot finish the fight," the newspaper quoted his lawyer Wolfram Schädler as saying.
According to the court spokeswoman, it is being discussed that instead of the father, the sister of the youth who was killed more than 40 years ago will appear as a joint plaintiff.
However, it is unclear whether the process will actually start on August 9 as planned.
The defendant's defense attorneys have lodged a constitutional complaint with the Federal Constitutional Court in Karlsruhe.
The suspect is currently in custody.
With new investigation methods, DNA traces of the alleged perpetrator, now sixty-three years old, could be secured in old evidence in 2012.
He is said to have raped and stabbed the seventeen-year-old from Hambühren near Celle in a forest.
On the way home from a choir rehearsal, Frederike got into a car as a hitchhiker.
By the end of 2021, no suspect in Germany could be charged again after a final acquittal in the same case unless he confessed to the crime.
But triggered by the Frederike case, a legislative reform was passed by the Bundestag and Bundesrat in 2021, which came into force on January 1, 2022.
According to a decision dated April 20, the Higher Regional Court (OLG) in Celle considers the retrial of the proceedings against the former accused to be permissible.