(CNN) -- Tim Hill still remembers the sound of wood popping as his house's attic burned. His brother, he says, had tried to set the home ablaze with eight people inside.
He also remembers the time when his mother awakened to a ghastly sight: his brother standing over her with a butcher knife.
And he remembers the message his brother sent him on Facebook, threatening to kill him.
When he heard that his brother, Michael Brandon Hill, had been accused of opening fire with an AK-47 inside a Georgia elementary school this week, Tim Hill said he was just "a little bit" surprised.
"Over the years of growing up with him, it almost seemed like eventually he would do something like this," he told CNN's Piers Morgan Live in an exclusive interview Thursday. "But not to this magnitude."
Authorities allege that Hill, 20, had about 500 rounds of ammunition when he entered the Ronald E. McNair Discovery Learning Academy outside Atlanta on Tuesday.
He barricaded himself in the front office, fired one shot inside the school and several more at police officers outside before he eventually surrendered, police said. Ultimately, no one was injured.
How did it come to this?
Tim Hill suggests that the system failed his family.
"I feel like there's just a whole lot more they could have done," he told CNN.
He said his younger brother used to be a normal kid. But something happened.
"Everything just started changing after doctors started messing with his medicines here and there and changing it up and putting him on a different one and institutionalized him multiple times to correct his medicine," he said. "It just escalated from there."
As the years went by, Tim Hill said he and other family members felt increasingly helpless.
"I felt hopeless at helping him," he said. "I tried many times growing up as a teenager to sit him down an talk to him."
But his advice never stuck. And earlier this year, his brother was arrested in March on a charge of "terroristic threats and acts" after threatening to kill him.
After pleading guilty to that charge, Michael Brandon Hill was sentenced in July to serve three years of probation and attend anger management classes as part of a plea agreement, according to Henry County court records.
It's not clear whether he started the classes. Henry County District Attorney James Wright said Wednesday there is no indication he has completed them.
Tim Hill said Thursday that he isn't sure whether he'll ever speak to his brother again. He said hopes the situation will be a reminder to people in the political, mental health and legal systems that more needs to be done.
People like his brother "need to be looked at more closely," he said.
"They need to be given more help," Tim Hill said, "instead of pushed to the side because the doctor thinks they're well."
CNN's David Mattingly, Martin Savidge and Greg Botelho contributed to this report.