Here in California they are required by law to assist you. Ask the police to issue a police report pursuant to section 530.5 on the theft of your personal identity. Do not expect over night service either. I filed mine close to two weeks ago and still do not have it. Let me tell you, if the crime happens to one of them they will not sit on it.
Time is money when combating identity theft.
If they will not give you a copy of the police report you are entitled to a summary of their investigation. Make sure you get the case number so you can track it. The case number may change if the investigation changes jurisdiction. Check with your state legislators for similar laws. You can click here to search for the US Postal Inspection Service near the criminals address.