Authorities have confirmed that the white powder sent to the office of Harvard Law Professor Alan M. Dershowitz in Hauser Hall last Wednesday tested negative for hazardous material, according to his assistant Sarah Neely, who had opened the envelope.

The substance’s identity? Starch.

Early tests had shown that the powder was negative for anthrax and other hazardous material, but authorities were not able to confirm the powder’s chemical makeup for another few days, when final lab results came in, Neely said.

Thirteen envelopes containing a similar white powder were received at the Wall Street Journal’s headquarters in New York that day. All the envelopes bore a postmark from Knoxville, Tenn.

The Journal had published an opinion piece on Jan. 2 in which Dershowitz, who is one of Israel’s most prominent defenders, supported Israel’s military actions in Gaza.

Neely said that FBI officials interviewed her Friday to determine what might have prompted the incident.

“This was the only connection we could think of,” Neely said.

Dershowitz receives hate mail on a daily basis, and his office is the only one at the Law School with bulletproof windows, Neely added.

The envelope Neely split open had “Alan” scrawled on the flap and contained a blank thank-you note, Neely said.

The Federal Bureau of Investigation in Knoxville is currently leading the investigation to determine who sent the powder and why, FBI spokeswoman Gail A. Marcinkiewicz said.

“We take very seriously these ‘hoax-threats,’” Marcinkiewicz said, adding that the person who sent the envelopes would likely face criminal charges if apprehended.

According to the U.S. Attorney General's office in Knoxville, the penalty for sending hoax-like threats is 5 years in prison accompanied by a fine. If the threat caused injury, this could be extended to 20 years. And if death resulted, the it could result in a life sentence.

As a precaution, Dean for Administration Francis X. McCrossan requested in an e-mail sent to the Law School community last Wednesday that “anyone intending to study or conduct business in Hauser not do so until further notice.”

Classes held in the building for the day were also rescheduled.

A second e-mail later that evening notified the Law School that law enforcement authorities had cleared the building for re-entry the next day at 7 a.m.

The Law School and Dershowitz’ office did not take further security precautions, Neely said.

—Staff writer June Q. Wu can be reached at junewu@fas.harvard.edu.