Law enforcement officials are awaiting lab results on a white powder that spilled out of an envelope addressed to Arizona Gov. Jan Brewer on Tuesday. The discovery of the powder briefly closed the State Capitol in Phoenix and sent Hazmat teams scrambling.
State police, Capitol police and the FBI are continuing to investigate after Phoenix's Capitol Tower was placed on lockdown for about an hour after a staffer opened the letter in the governor's offices there, the Arizona Republic reported.
A spokesman for the FBI's field office in Phoenix said a laboratory run by the state's Health Department has conducted tests on the white powder. He could not confirm whether the envelope was hand-addressed or contained any note or threat in addition to the substance. No one was sickened by the powder.
The incident has heightened tensions in Arizona, where protesters have targeted Brewer since she signed a controversial immigration bill into law last month.
Under the terms of the law, Arizona authorities are required to question people about their immigration status if they are suspected of being in the country illegally. Critics say the law will lead to racial profiling in Arizona, which has a large Hispanic population and shares a long border with Mexico.
Brewer has become the law's symbolic stand-in, widely vilified during pro-immigration protests that hit a peak on Saturday, the annual celebration of May Day. Some demonstrators in Dallas carried signs depicting Brewer in Nazi uniform with her arm extended in a stiff Nazi salute, the Associated Press reported.
Officials in Arizona's Capitol Police Department and state police did not respond to queries from FoxNews.com about whether investigators were considering possible ties to the immigration uproar.
Brewer has been pushing for stiffer enforcement along the border, accusing the federal government of ignoring growing violence from drug smugglers she says are "invading" the state through gaps in the border fence. One-third of all illegal immigrants cross into the U.S. through Arizona, according to government estimates.
Lawmakers opposed to the tough new immigration measure have also been singled out. Rep. Raul Grijalva, D-Ariz., received death threats over his opposition to the immigration law and was forced to close his district offices on the day Brewer signed the measure. He has since sent a letter to President Obama urging him to "limit [federal] cooperation with Arizona officials in their enforcement."
During the brief scare on Tuesday, no one was forced to evacuate the Capitol, though authorities quarantined the building as police and firefighters swarmed the area.
Brewer was not in the Capitol Tower when the envelope was opened; she was scheduled to be about 115 miles away in Tucson for all of Tuesday, according to publicly available documents.