Would he have even been arrested if he'd done this in 1865?
Or 1905?
Or 1955?
Probably arrested, but not found guilty.
Back then, the all white courts of the South usually didn't convict a white person for killing blacks.
Even in the mid 60's they didn't do it.
Remember the movie "Mississippi Burning"? In real life those men were all found not guilty in state court (actually, the state refused to even prosecute them). The Feds had to come in and charge the men with Civil Rights Violations. That's the only way those white men went to jail.
Things are different now despite what the media might portray.
The prosecutor won't need the Feds help in finding this kid guilty. Besides, he already confessed.
The question is whether or not they will seek the death penalty for him.
Which raises another interesting question. Most Libs are against the death penalty, while most Conservatives are for it. South Carolina has the death penalty, North Carolina does not; which may or may not be why that's where he fled to, although he didn't fight extradition.