Something don’t seem right about the Texas mass shooter shaking hands with police

Why was the Wilmer-Hutchins, TX mass school shooter, who injured four people and calmly turned himself in to police, allowed?? able to?? shake hands with the arresting police officers as he was being taken away to jail?

Why would those officers want to shake his hand?

Why does almost every school shooting have shady sh*t like this surrounding it?