Seidel spent almost his entire career at Siemens. In 1985, he took over its communications division. He said his predecessor taught him how to win contracts with Nigeria's state-owned telecommunications company NITEL with bribes, a practice which until 1999 was legal in Germany.[1]
Colleagues referred to him as the king of Nigeria.[2]
In 2005, Seidel stepped down.[1] Before he left Siemens in 2004, he had earned 300.000 Euros per year.[2] In 2006, German authorities raided the Siemens headquarters and Seidel confessed his role in the bribery scheme. In 2007 his name was entered on World-Check.[3]
In 2008 Seidel faced trial in Germany for bribing foreign officials in the "biggest bribe scandal in German history". He received a one-year suspended prison sentence, fine and costs of 240,000 euros.[1]
In 2010, the Nigerian Economic and Financial Crimes Commission summoned him to appear at the Abuja High Court in connection with the Siemens 17.5 million Euros scam, but he remained at large.[4]
In 2008, Seidel founded a shell company on the British Virgin Islands, which in 2009 bought four real estate objects in Dubai, amongst them a mansion on The Palm Jumeirah, as revealed in the 2021 Pandora Papers.[2]
Seidel has held more than 54.5 million Swiss francs ($41.9 million) in 6 Credit Suisse bank accounts, one of which was active until at least 2016, as revealed in the 2022 Suisse secrets.[1] Credit Suisse never reported Seidel to the German prosecution as suspicious, even though his salary did not explain the amount in his Credit Suisse accounts.[2]