Have the victim complete the FTC Identity Theft Affidavit. http://www.ftc.gov/bcp/edu/resources/forms/affidavit.pdf A copy of this should be attached to the Police Report and filed with the credit bureaus, credit card companies, collection agencies, and any other companies where accounts have been compromised.
Ask victim to forward regular and electronic mail (use the "forward" function) if applicable to the identity theft crime.
Keep in mind that ID theft is an emotional as well as an economic crime.