From Jerusalem Post:

In its Sunday issue, Spiegel reported that the talks were initiated at the behest of the West German government, located at the time in Bonn, for fear that Black  September would commit additional acts of terror on German soil.

According to the report, just several months after the murders, the government  proposed a secret meeting between a Black September official and then-German foreign minister Walter Scheel, the aim of the which was to create a “new basis of trust.”

Germany’s government demanded a quid pro  quo: the PLO would cease terror attacks on German soil in exchange for a political upgrade of the PLO. In addition, the German government would  pull the plug on any criminal charges for the murders in Munich.