SurfNturf-I agree but I also wanted to add that you can write the book as intended and you may have legal ground if you can prove that the information is truthful and dissseminating this information is a public safety issue.
This also falls into the privilege defense which means that you had to offer this information as a duty to other people. The last defense also pertains to the person's reputation as it currently stands.
If the person already had a bad reputation as a result of their past actions then chances are that any defamation action against you will not be successful.
For example, if you write a book about a person who was charaged and convicted of sexual assault then all of the defense arguments come into play because it is a measure of public safety to let other know about this person's violent past.
Also, the fact that the person was convicted means that the charges were true and the fact that the person already suffered from a damaged reputation was a direct result of his previous actions not your book.