We know that Smiths doesn't want to be at the school, we know Oscar is Smiths body guard, we know it is illegal to start someone else on fire, we know Smiths has been known for lying and we know that Smiths doesn't like Oscar.
We can infer with this information that Smiths probablly started the fire to either get away from the school or get Oscar fired and maybe even in jail.
"Luke dug into the mattress and pulled out two identification cards. Fake ones. Or were they?" (71)
We know that there are lots of kids with fake identities in Hendricks school, we know that Smiths is Lee Grant's brother and Luke is pretending to be Lee Grant so we then know that their parents are willing to give up the kids identities and we also know that Smiths didn't seem to know how to act normally.
We can infer with this information that Smiths is possibly and illegal 3rd child too.