If you find yourself the target of a stalker or harasser who has threatened your life and plans to post personal information about you or related parties that could bring you or anyone you care about harm, do the following.
1. Leave a report with your local law enforcement about the incident. Even if it comes to nothing, you can sleep easy at night knowing the police are aware you have been threatened and you can provide them updated information should your situation change at any time.
2. Leave a report with the FBI or the equivalent organization in your country of residence. If the party in question has done these acts primarily via means of the Internet, you can report their activities here.
3. Keep archives of all the threats you have received and be prepared to add them to any existing reports you have submitted or provide them to proper law enforcement officials. DO NOT respond to them, merely archive them if at all possible, and keep copies of everything.
4. Do whatever you can to avoid antagonizing or responding to further abuse from the harasser. If they are stalking you via social media, do not respond to their provocations and ignore any attempts they make to further threaten you. Report them to the appropriate parties at these services and have them deal with it.
5. Keep as much personal information as you can safe from their reach. A common tactic of those who attempt to stalk people is to spread their personal information far and wide to deny them privacy and to have them live in fear as a result, so if you can prevent them from discovering your real name, face, and location especially, take any and all means needed to make sure this information does not fall into their hands.
6. If you believe you are in imminent danger, dial 911 or whatever your country's equivalent service is.