The Siege: Alan Gregory, Book 17

and the FBI's vaunted Hostage Rescue Team. Attention quickly focuses on the fortress-like tomb of one of Yale's secret societies. Suspended Boulder police detective Sam Purdy soon finds himself in New Haven, where he is quickly snared by an unlikely pair of Feds: FBI agent Christopher Poe and CIA analyst Deirdre Drake.
Sam, Poe, and Dee join together, desperately trying to solve the riddle of what is going on inside the windowless stone tomb on the edge of campus. The clock is pounding in their ears. The unknown enemy is playing by no known rules...is making no demands...is refusing to communicate with the hostage negotiator...is somehow anticipating every FBI move...is completely unconcerned about getting away...

And...is sending students, one by one, out of the building's front door to die.