They can (very easily) pull the IP address of the email - that's something you can't "fake." Once they link the IP address to you, you're caught.
1) Talk to an attorney regarding the contents of the email ASAP.
2) Do not discuss this any more on any other forum. Less said, the better.
3) See #1
David gives very good advice. I would not wait for this to come to a head. I would go ahead and make an appointment with a local, criminal attorney tomorrow.
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