On December 14, 2015, Kengeter obtained 60,000 shares worth 4.5 million euros ($4.8 million) in the company. He bought the shares as part of a remuneration program for the company's board of directors.
Just two months later, on February 23, 2016, it was announced that Deutsche Boerse and the London Stock Exchange (LSE) were in discussions about a merger, which caused the share price of both companies to rise significantly.
Kengeter and chairman of the supervisory board Joachim Faber have denied any wrongdoing, claiming that negotiations about the merger only began in the second half of January.
Frankfurt prosecutors have asked for information about all discussions among the Deutsche Boerse leadership from summer 2015.
According to German newspaper Der Spiegel, new information has already come to light which casts doubt on Kengeter's claim that the merger hadn't been in the works when he bought the shares.
Kengeter allegedly discussed the possibility of a merger with the LSE with Lars-Hendrik Roeller, economic adviser to Angela Merkel, in November 2015, before he bought the shares.
On Friday, Der Spiegel reported that Kengeter told Roeller that the merger had been agreed upon in principle, but the British government would only give its approval if the group's headquarters was based in London. Roeller responded that the German government would oppose such a move.
On Friday, Thomas Schaefer, the finance minister of the German state of Hesse, where the country's financial center Frankfurt is located, called for the company's headquarters to be located there instead of London.
"The reasons for the headquarters being in Frankfurt are crystal clear," Schaefer said; "Those involved in London must recognize, also in their own interests, that it would not be a good idea to keep the plans as they are now," the minister added.
The merger proposal has yet to be approved by authorities in Hesse or the EU. The EU Commission is currently conducting an investigation to decide whether the merger of Europe's two largest stock exchanges could hamper competition, and is scheduled to announce its decision on April 3.
