A police officer holds tape to keep people out from an area at Harvard University in Cambridge, Mass., Monday, Dec. 16, 2013 (Photo: AP)

Police officers secure an area at Harvard University in Cambridge, Mass., Monday, Dec. 16, 2013 (Photo: AP)

A security officer guards a gate and keeps people from Harvard Yard at Harvard University in Cambridge, Mass., Monday, Dec. 16, 2013 (Photo: AP)

SWAT team officers arrive at a building at Harvard University in Cambridge, Mass., Monday, Dec. 16, 2013 (Photo: AP)

A pedestrian walks by as SWAT team members assemble outside a building at Harvard University in Cambridge, Mass., Monday, Dec. 16, 2013 (Photo: AP)

Tactical police assemble outside a building at Harvard University in Cambridge, Mass., Monday, Dec. 16, 2013 (Photo: AP)

A police officer looks out of an entrance to the Science Center at Harvard University in Cambridge, Massachusetts, December 16, 2013 (Photo: Reuters)

State and local police respond to reports of explosives at Harvard University in Cambridge, Massachusetts, December 16, 2013 (Photo: Reuters)

State and local police respond to reports of explosives at Harvard University in Cambridge, Massachusetts, December 16, 2013 (Photo: Reuters)

State and local police respond to reports of explosives at Harvard University in Cambridge, Massachusetts, December 16, 2013 (Photo: Reuters)