Earning a J.D. was an early goal for Deputy Gov. Christian L. Mitchell, who completed law school last month.Mitchell, 33, traces his ambition to practice law back to his introduction to the criminal justice system when his aunt, Donna Gist, was wrongfully convicted in the death of a five-month-old boy in the late 1990s.With the help of attorneys Thomas M. Breen and Todd S. Pugh, Gist’s murder conviction in DuPage County court was overturned in 2000.“That’s what made me initially want to be a lawyer …