BARROW COUNTY, Ga. — A Barrow County grand jury is expected to convene on Thursday morning where they could hear the cases against Apalachee High School shooting suspect Colt Gray and his father, Colin Gray. Both are facing murder charges.

Prosecutors are seeking formal indictments against the father and son.

This comes just one day after Colin Gray appeared in court where Georgia Bureau of Investigation agents and Barrow County investigators testified about the details of what they’re calling Colt Gray’s plan to kill several people in the school.

They detailed drawings he’d done, what they described as an “obsession” with school shooters and even that he was trying to create a “school shooter outfit.”

The 14-year-old is accused of taking an AR-15-style rifle into Apalachee High School on Sept. 4 and opening fire killing two students and two teachers. Nine others were wounded.

Investigators say Colin Gray bought the weapon for his son as a Christmas gift just months after being investigated for a separate school shooting threat last year. They say he also bought his son ammunition, a larger magazine for his gun and a tactical vest.

GBI agents testified on Wednesday that Colt Gray got the rifle into the school by disguising it as a school project.

“We determined that the rifle was protruding out of his book bag – and part of the rifle that was showing was concealed with a rolled-up poster board,” GBI Special Agent Lucas Beyer testified.