without an identity, I don't know how seriously any law enforcement agency is going to take this.
IANAL as usual but it shouldn't take much to subpoena Amazon for hosting/payment details.
http://www.amazon.com/gp/help/customer/display.html/?nodeId=508088How to Serve a Subpoena
If you have a subpoena to serve on Amazon, please note that Amazon does not accept service via e-mail or fax and will not respond to the subpoena. All subpoenas must be properly served on Amazon.com, preferably by mailing the subpoena to Corporation Service Company (CSC), Amazon's national registered agent. Please find below the Washington address for CSC (the CSC office in your jurisdiction may be located through the Secretary of State's website):
Amazon.com, Inc.
Corporation Service Company
300 Deschutes Way SW, Suite 304
Tumwater, WA 98501
Attn: Legal Department - Subpoena
Please note also that providing detailed and accurate information at the outset will facilitate efficient processing of your request. That information will include, for example, e-mail and/or credit card number used to make purchases for retail purchase information; the name, e-mail, and physical address of a seller for seller information; Kindle serial number for Kindle information (please note we do not have GPS location information); and IP address and complete time stamp for AWS information.
Subpoena comes from a court, or from an attorney on behalf of a court in which there is an active case. Seems impossible you can get to a point where there is a subpoena power to obtain this information, because you're again talking about a civil remedy which a court will dismiss before you get to that point. Civilly, you will not be able to get this information.
But perhaps on criminal charges the authorities could pursue this, because AWS would be pretty good information about his likely identity considering he most likely paid with a credit card. I hadn't thought of this before. This would be worth following up on if you wanted the authorities to try to track him down. Still a long shot, and you would need someone to actually have the resolve to make this happen by filing a complaint.
I don't think you'd get much from the credit card details as they most likely used prepaid credit cards or another form of anonymous payments. The IP addresses might be very interesting though..
Aside from the hosting company AKs ISP(since DMF 'used' his IP address) might be able to shed some light on what incoming and outgoing connections were made from his IP address, I don't know how things are in the US but where I'm from ISPs keep logs up to a year.