After qualifying in 1973, Haag worked as a lawyer in Heidelberg and briefly defended Holger Meins in 1974 and Andreas Baader in 1975 during his trial at Stammheim.
[1] Haag was known to be a leftist terrorist sympathizer, and supposedly while he was working as a defence lawyer, he would act as a messenger, passing on information, between different members of the RAF.
His crimes became more substantial however and in 1975 he was arrested for smuggling weapons through Switzerland (with the help of Elisabeth Von Dyck) and served six months in a detention centre.
For a period between 1975 and 1976, Haag underwent guerilla warfare training in a Southern Yemen camp, before returning to West Germany.
In the vehicle they found weapons and cryptic documents that revealed details of the Hanns Martin Schleyer kidnapping, which were deciphered at a later time, only in hindsight.