It looks obvious

Several buildings at Brandeis had been cleared, including an adjacent Waltham elementary school. So law enforcement officials were eager to make speedy headway in identifying both the perpetrator and the threat’s credibility, and had quickly moved to secure evidence at the Newton library.

What they had not anticipated, however, was that their search would be abruptly sidetracked when Kathy Glick-Weil, the library’s director, informed them that no one was searching anything without a warrant from a judge — this, despite the obvious urgency to act in an instance when a perpetrator was fleeing, time was passing, and a potentially catastrophic incident became more imminent by the minute.

The would-be terrorist who threatened Brandeis University from a computer in the Newton library, far from relying on an expectation of privacy and the "right to be left alone" while sending surreptitious emails from a public building, loses those constitutional protections once he conducts his informational transactions in public. As Heather MacDonald, a Senior Fellow at the Manhattan Institute for Policy Research, recently testified before the United States Senate Select Committee on Intelligence,

"Like it or not, once you’ve disclosed information to someone else, the Constitution no longer protects it. This diffuse-it-and-lose-it rule applies to library borrowing and Web surfing as well, however much librarians may claim otherwise. By publicly borrowing library books, patrons forfeit any constitutional protections they may have had in their reading habits."

These are not merely philosophical debates because the use of libraries by terror suspects has been well documented. Reports were received from Florida directly after September 11 from the Delray Beach Public Library, where reference librarian Kathleen Hensman claimed that Mohald Alshehri, listed as a hijack suspect, had used the library’s computers. Similarly, library patrons in the Hollywood, Florida area, where five of the 9/11 suspects had stayed prior to the attacks, identified Mohammed Atta, another of the hijackers, as having used two of the area’s libraries.