If you are referring to the apparent discrepency between the plural pronoun, their and its singular antecedent, person, there is an explanation.
Modern English has traditionally used the gender-specific pronoun, his in these types of constructions where person could refer to a man or a woman. Many modern writers consider this to be sexist, or anti-feminist, so today more and more style manuals recommend using the non-gender-specific plural pronouns, they and their.
Any of these is considered correct today (at least in American English).
1. If someone is arrested for a crime, then he should have a fair tiral.
2. If someone is arrested for a crime, then he or she should have a fair trial.
3. If someone is arrested for a crime, then he/she should have a fair trial.
4. If someone is arrested for a crime, then they should have a fair trial.
Personally, I hate sentence 3 and would never use that form. In my own writing, I try to avoid these constructions, but when I can't, I just pick one and stay with it throughout the entire writing.