what changes had the father observed in dicks behavior after this event?

is the event the car accident mentioned in Part 1?

His criminal (or “antisocial”) tendencies are in some ways harder to explain than Perry’s, or at least, they don’t have roots in childhood neglect. Dick has a solid home life, and genuine affection for parents and brother. Economic duress seems to have played a bigger role in determining Dick’s chosen path, but the decisive event seems to have been a head injury he received in a car accident, after which, according to his father, he “wasn’t the same boy.”