He's accused of taking payoffs, gifts and vacations in return for government contracts and leases.
The investigation initially focused on bribes exchanged for licenses for unqualified truck drivers, but it was later expanded to include other corruption.
As governor, Ryan became known worldwide as a leading critic of the death penalty. The republican served as secretary of state from 1991 to 1999.
Ryan is the 66th person charged in the investigation. In all, 59 people and his campaign committee have been convicted so far.
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