Wealth?

Drug deals. How did you miss that? Serge was a mole for the police during his time in prison. In exchange the police kept a blind eye on him doing drug deals. He was the middle man between Edmond and the other mob but cheated on Edmond which set the entire plot going.

When he was young they committed tons of bank robberies but to stay under the radar they lived in the shitty trailer camp; they hid the money and did not spend it.

At one point in his youth one of the robbers and his younger brother are strangled to death in the attic by other members because they were splashing their cash around and attracting attention.