If Twitter had turned over the user's identity at the first request, it could have been liable for any mistake or potential invasion of privacy, according to Jennifer Granick, the director of civil liberties for Stanford Law School's Center for Internet and Society.
"The law prohibits providers from turning certain information over voluntarily and, if they do, they can be sued," Granick said Tuesday. "But the government can compel the information from the provider with varying degrees of legal process depending on what the information is. When it's the name associated with the account, the government can get that with just the subpoena."
The federal law is part of the Electronic Communications Privacy Act, passed in 1986. There are exceptions to the law, Granick said. Exceptions can be made if there's a threat of serious bodily injury or death. But that first decision is up to the provider.
When another Twitter user asked the threatening tweeter on Aug. 3 whether he or she had undergone a change of heart about the prospective shooting at the Midtown Manhattan theater, the person replied, "no I had last minute plans and I'm in Florida rite now but it'll happen I promise I'm just finishing up my hit list."
The Twitter user made frequent references to his or her "hit list," making threats against many celebrities, including Ellen Page, Perez Hilton, Wendy Williams and several members of the Kardashian family.