J. R. Rain - Dark Horse (Jim Knighthorse Series, Book 1)

When high school student Derrick Booker, the only black student at a posh Orange County high school, is accused of killing his white girlfriend, ex-college football hero and detective Jim Knighthorse is hired to dig a little deeper into the murder. It doesn't take long for Knighthorse to realize that not all is as it seems at tranquil Huntington High, from a band director who preys on the innocent to a vice-principal with a secret agenda of her own. Not to mention someone's hired a professional killer to keep Knighthorse permanently off the case.
As the investigation continues, Knighthorse's personal life is shattered by the discovery of new evidence relating to his mother's unsolved murder, a murder dating back twenty years. Reeling from the discovery, a determined Jim Knighthorse sets out to bring two killers to justice.