When Christopher arrives at the police station, they make him empty his pockets, and he describes in detail what he had with him
They try to take his watch, but he screams, so they let him keep it.
Then they ask him if he has any family. Short answer? Yes. Long answer? Everything Christopher says: he tells them about his father and his uncles and his grandparents and, well, way more information than they need to know.
He also tells them (and us) that his mother is dead.
They ask for his father's phone number, and put Christopher into a cell. While he's in there, Christopher figures out the volume of air present in the cell, and also works out what would be the best way to escape (if he were in a story, that is). Those are some major math chops he has.
He also wonders if Mrs. Shears told the police that he killed her dog. If she did, he figures she'll go to prison when they find out she was lying.