Hello,
A lot of information can be found out about an IP address including the geographic location and the ISP that owns it, but it's usually not possible for anyone but the ISP to know for certain which customer is using an IP address.
To get the IP address from an email you can check the
full email headers.
You can use this site to check what ISP owns an IP address -
ARIN: WHOIS Database Search
With the full email headers, IP address, and whois lookup you should have enough information to call your local police department and have their cybercrimes department investigate the issue further. They will have the power to contact the ISP and get the private customer data that the ISP most likely will not be willing to release to you.
You mentioned you already know how to make a report. Other things that may or may not work for you while trying to confirm the identity of someone include doing a google search for the IP address and seeing what comes up, or contacting the person you suspect has an IP address with a fake IM or Facebook account. Lead those to an email conversation with the suspect and see what IP address they are using. Don't forget they'll be able to see your IP address too.
If at any time you feel you are in danger please call the police immediately.
-Raymond