That murder was racist and it did expose institutional racism and discrimination, so why the quotation marks? Both racism and institutional discrimination are real things in the world. And neither things were in doubt in this case. So, again, why?
Let me make a hypothesis here: we insert quotation marks around factual statements when they somehow reveal that minority / marginal points of view turned out to be objectively correct after all.
One of the marks of privilege is to have one’s privileged point of view readily accepted as factual and objective and not marked by bias whereas the points of view of disadvantaged categories tend to be dismissed as overreactions, exaggeration and overall lack of objective perspectives. Therefore, we put quotation marks as a marker of point of view rather than factual statement.