Dear told officers he threw the brick in an act of self-defence on 16 June, police said.
He said his father drove the van in his direction, in Windsor Road, Newark, and this prompted him to throw the brick to try to stop him.
The object then hit his father in the head, resulting in a large cut to his forehead.
Police said Thomas Dear Senior then drove away from the scene and later down Lombard Street, where he suffered a cardiac arrest at the roadside and was pronounced dead at the scene just before 18:00.
The pair were captured on CCTV footage in a “prolonged argument” before the fatal throw took place, the force said.
Dear was seen throwing pieces of a broken plant pot at his father, with Mr Dear Senior then approaching his son wielding a garden fork, officers added.
A Home Office pathologist who conducted a post-mortem examination linked the head injury sustained from the brick to the cardiac seizure that led to Mr Dear’s death.
Det Ch Insp Ruby Burrow, of Nottinghamshire Police, said: “Whilst Dear may not have set out to intentionally kill his father, his dangerous and deliberate actions have resulted in the most devastating and irreversible of consequences.
“The impact on Mr Dear’s family and friends has been simply immeasurable, having to endure the loss of a loved one in such sudden and traumatic circumstances.
“I hope the conclusion of this investigation and subsequent court process will help to bring some closure.”