There was a topic where someone summarized it. His death was suicide.
Indeed and he was walking in the opposite direction from which his brother was coming from. The only reason he smiled sadly was because he was happy and sad to see his brother whom he loved so much for the last time. He wasn't planning to escape from just his brother, but from everyone else as well and found the solution in death. The letter left to his wife and the money left to his brother is proof of it. It was his last wish or something like that said his son, so kind of like a testament and inheritance after a persons death. He knew...... Because he planned it all..... From the start.
I don't think he killed himself... he hear his brother and decided to go to where he was... he was happy when he hear him...
I'm pretty sure he didn't saw the truck... or he won't see so happy when he hear his brother!!!