Unfortunately, information about users can only be handed over to duly appointed authorities. If you are receiving threatening messages, please report this issue to your local police. If an investigation ensues, a subpoena may be provided requesting information for a user account.
In the mean time, you can prevent further messages from being sent to your telephone by visiting
http://textr.us/anonytext and added your number to the Block List. This prevents messages from being sent to you by any AutoSMS service.