Given that whatever went down involved two of the other kids ending up in foster care, and the youngest still says the oldest "ruined his life", I'm pretty sure that "it's a serious crime" is a reasonable assumption.

Sure, our criminal justice system is bullshit in multiple ways, and so is child services... but honestly, with all the shit in this letter, I'm going to err on the side of trusting, at least, that the accusations were probably serious ones.