Music Case

The Police Academy finally gets Inspector Strong into a one-day presentation of his choosing. The Chief of Police is surprised but happy.
It will be for a wide range of staff from police Chiefs to clerks. The attendees will be there on time or get locked out. Dress properly or get locked out. A few who do not follow the rules are made to wait.
The Inspector walks on stage and throws the official report in the trash can to start fresh. The Greenwood shooting, known as the Music Case is reviewed from the time of the first call. Many whys are asked, and the Inspector expects those in the seminar to take what was found and solve the case just as his detectives did.
There were witness, crowd control issues, family members, and one dead music teacher all to handle.
It is a treat as Detective Rage leads part of the seminar. Detective Smith has his share.
At the end of the seminar each attendee will have their own case file on their lap. The case appears to be going into the cold case file for all those in the seminar. The Chiefs know a suspect was arrested.
How was it closed from what is in their booklet and the discussions?