Let’s look at minimum wage at the time he was imprisoned: $3.35/hour. Make that his wage the entire time he was in prison. After the first 40 hours a week he’d get OT, so it comes out to about $3,300/month. Since he wasn’t able to spend that money, let’s put a monthly payment into the market, with an average return of 7%…
That would put him at $6,587,619.39 at the end of 37 years if we value his freedom at the 1987 minimum wage.