Tim Hill told CNN's Piers Morgan on Thursday that when he and Michael Brandon Hill were growing up, his brother was "like any other kid." It was during his teenage years when he started to change.
"Once he started hitting his teenage years, something happened with him. Everything just started changing after doctors started messing with his medicines here and there, and changing them up and putting him on a different one and institutionalizing him multiple times to correct his medicine. It just escalated from there," described Tim Hill.
He said his brother set fire to the family's home when eight people were inside sleeping. The blaze was caught before it spread. In another incident, their mother woke up to find Michael Hill standing over her with a butcher's knife.
"My stepfather and mother ended up having to lock up...like all the knives in the trunk of the car, just to protect everybody in the home," Tim Hill said.
Tim Hill also confirmed that his brother threatened his life on Facebook, prompting him to call police. He said he feared for his life.
His comments came two days after his brother arrived Tuesday at Ronald E. McNair Discovery Learning Academy in Decatur, a suburb east of Atlanta, armed with an AK 47-style rifle and nearly 500 rounds of ammunition.
School bookkeeper Antoinette Tuff helped persuade Michael Hill to surrender to police following the frightening standoff and shooting.
On a 911 call recording released on Wednesday, Tuff can be heard relaying messages from Hill to DeKalb County emergency dispatcher Kendra McCray before convincing the gunman to surrender. She tells the dispatcher that Hill said he wasn't there to hurt the children but wanted to talk to an unarmed officer.
"He said, 'Call the probation office in DeKalb County and let them know what's going on,'" Tuff is heard telling the dispatcher. "He said he should have just went to the mental hospital instead of doing this, because he's not on his medication."
No one was hurt, but police said the suspect shot at the floor and exchanged gunfire with officers who had surrounded the school, which has 870 students in pre-kindergarten through fifth grade.
With bullets flying, Tuff urged the gunman to come back inside and give up. She told CNN's Anderson Cooper on Thursday night that she knew he was not in his right mind.
On the program, she had a tearful on-air reunion with McCray, the dispatcher who stayed on the phone with her. Tuff also received a call in the network's makeup room from President Barack Obama. She said Mr. Obama wanted her to know how proud he was of her.
McCray described Tuff as "a true hero" on the program.
"You did so great. I've never had a caller where the caller was so calm and so confident in what they were saying and so personable. You made my job a whole lot easier," she said.
Hill is charged with aggravated assault on a police officer, terroristic threats and possession of a firearm by a convicted felon. Police declined to discuss what he told them when questioned. His motive remains unclear.