In Michigan can the act of "aiding a fugitive" prove the charge of manslaughter? Sometimes laws are bizarre.
In principle, depending on the context, sure.
I wouldn't say "prove," but an element of the criminal negligence could be knowing the character of the killer, knowing the killer intends to kill, and doing nothing about it.
Negligence is a broad concept - act as a reasonable person would in the same or similar circumstance is the standard under civil law. Things turn toward criminal when a person is indifferent about death and mayhem that a person has the ability to mitigate.
Tough thing here is we don't have any handle at all about the kid's behavior over say the last year. It's possible that no reasonable person would have expected this kid to act out this way.
Similar with school admin - maybe they saw things as kid having a bad week, need to get some counseling.