April 1976, $4 million in cash was stolen in the Great Bookie Robbery, the largest heist ever. Today some 35 years later, you'd need to steal $50 million to equate to $4 million in 1976.
You could also buy about a 1000 houses for 4 mil back then. A 1000 houses would cost you about 400 million now. Edit - bad maths....