The Federal Prosecutor's Office in Karlsruhe announced on Thursday that genetic material unmistakably belonging to Becker had been found on several envelopes of letters claiming responsibility for the attack on April 7, 1977.
Buback, a strong opponent of the leftist terrorist group during his term, was killed along with his driver Wolfgang Göbel and a judicial officer, Georg Wurster, on the way to the court house in Karlsruhe. A motorcycle pulled up to Buback's Mercedes at a stoplight, and a passenger on the back opened fire with an automatic weapon.
The latest revelations come as a surprising turn in the ongoing investigation into one of the highest-profile political killings carried out by the RAF. Only last year, investigators said testing on a motorcycle glove, helmet and jacket found after Buback's death had ruled out any connection to Becker.
The 57-year-old Becker was released from jail some 20 years ago after serving several years for RAF related crimes.
Former RAF members Christian Klar, Knut Folkerts, Günter Sonnenberg, Brigitte Mohnhaupt have all been convicted collectively of the Buback murder, but authorities remain unsure of who fired the deadly shots. Michael Buback, the son of the murdered prosecutor had repeatedly named Verena Becker as a possible suspect.
The federal prosecutor's office has also been investigating Stefan Wisniewski, after ex-terrorist Peter-Jürgen Boock implicated him as the possible shooter.
Buback's murder was the first crime in a series of terrorist acts by the militant communist RAF group in their radical opposition to the West German government that came to be known as "German Autumn" in 1977.