From the story:
"Miller joined the police department in September and graduated from the city police academy earlier this year."
This can't look good to the Grand Jury. Less than a year on the force, and the first time he draws his gun in the line of duty, he puts 4 bullets into this kid.
He wasn't trying to coordinate with anyone. His partner had his taser drawn, and his Commander had told him not to enter the building. Maybe he could go to bartending school?