They charged Kyle with murder before doing even minimal investigation. A 1st year law student can easily show Kyle defended himself against a violent attacker and the subsequent vigilantly mob that formed. Many valid points can be made about him being under age or that he shouldn't have been there at all. But, none of these points takes away his right to self defense if attacked.
They step through the facts here:
https://www.youtube.com/watch?v=NSU9ZvnudFE&feature=youtu.be&fbclid=IwAR00QmsZcEB7WSDw2-cVNWXDcxYNZU3zvkXJ89_CoLXiOve8ZXT2sWrkb-4&bpctr=1599006135
The police didn't charge him, the prosecutor did. Police don't go about their jobs with a political affiliation or agenda, but prosecutors do. This case is weak for doing any time. Law and order was restored among that mob, wasn't it?