The Georgia Bureau of Investigation also arrested the teen's father, Colin Gray, on Sept. 5, and prosecutors have charged him with two counts of murder, four counts of involuntary manslaughter and eight counts of child cruelty.

The teen suspect was questioned last year about online threats, though nothing conclusive emerged. Many local police departments lack the resources to take deeper looks at suspicious actors.

Annie Brown, Colt Gray's aunt, told 11Alive Marcee Gray called the school that day to warn about the possibility of an "extreme emergency."