This (paywalled) article in Süddeutsche Zeitung has a lot more background info, for instance about Hanning's Russian connections.

https://www.sueddeutsche.de/politik/hanning-festnahme-spiona...

In 2013 he was a defence witness for the oligarch Oleg Deripaska who was then tied to Putin. He was also on the board of companies such as PNB Banka (operated by a Russian Grigory Guselnikov). Also connections to many shady "security consulting" firms, among them "Prevent" who were suspected to have planted child porn with a manager of HSH-Nordbank. Incidentally child porn was also planted with the husband of Christina Block in Denmark, a case in which Hanning is also involved.

On the angle of Azerbaijan who allegedly bought Hanning's secrets it's interesting that in the past there were several court cases about corruption against German politicians. It's summarised in the so called Aserbaidschan-Affäre (Azerbaijan Affair) https://de.wikipedia.org/wiki/Aserbaidschan-Aff%C3%A4re

See also https://www.esiweb.org/proposals/caviar-diplomacy