Reece Messer, 17, was released on bail and warned by police for targeting the 18-year-old Olympian following his fourth place finish in the synchronised diving on Monday (July 30).
Among the tweets he sent to Daley were a hurtful reference to the athlete's late father and a threat to "drown [him] in the pool".
Speaking in the wake of the scandal, 58-year-old Norman Messer has apologised to Daley for the actions of his son, who he claims has "gone off the rails" due to his struggle with ADHD.
"Reece badly needs help. I'm heartbroken this has happened to him," he told the Daily Mail. "I think the police should be involved, but he doesn't know what he's saying. He just doesn't think about it.
"We've had a long history with Reece. It all started when he was about 8 years old, he was quite normal up to that point. Then he started going to school, insulting the other children, saying things like 'your mum's a prostitute' to the other little boys.
"After that there were other problems in school. He's just gone off the rails. He suffers from ADHD. But he won't take his medication.
"I just want to say sorry to Tom Daley and wish him every success in the future."
Daley has not commented publicly on the arrest, but is said to be taking the scandal "in his stride".
Photo gallery - London 2012 in pictures:
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