The 'evil' father of Georgia school shooting suspect Colt Gray deserves to die for turning his son into a mass murderer, the boy's grandfather has said.

Colin Gray faces four counts of manslaughter and two counts of second-degree murder amid claims he gave his son the AR-15-style rifle used in the massacre at Apalachee High School on Wednesday.

Gray's ex-father-in-law said the 14-year-old was 'driven by his father to do what he did' as it emerged that Colt's grandmother visited the school outside Winder just hours before the shooting to discuss his behavior.

'Spending 11 years with that son of a b***h screaming and hollering every day, it can affect anybody,' Charles Polhamus, 81, told the NY Post.

'He needs the death penalty.'

Gray, 54, appeared in court on Friday after he was arrested over his role in the shooting that killed two students and two teachers, and left nine injured.

The alleged gunman's parents split in 2022 after they were evicted from their home and Colt was living with Gray when the shooting took place.

'Colt has to pay for what he did, but I'm telling you, he was driven, no question in my mind,' Polhamus said from his home in Fitzgerald.

'Colt is like a lot of young kids these days with the tablets and some of the garbage they pull up, the blood and all the fighting.

'If you don't think that has an impact on young kids, you're missing the boat, and that was also part of Colt's problem.

'It's part of it — and living with a dysfunctional dad who was a screamer and a hollerer.

'No question about it. Prior to going through this, he was a good kid. I will preach that forever.'

Polhamus said his wife Deborah had gone to the school a day before the shooting as family concern about Colt mounted.