Authorities in Arizona are continuing to search for the person responsible for sending a letter containing a suspicious white powder that was mailed to Gov. Jan Brewer earlier this week.
Special Agent Manuel Johnson of the FBI's Phoenix field office told FoxNews.com that the probe into the letter, which contained a non-toxic substance, is ongoing. Johnson declined to comment further, and refused to address whether investigators believe the incident is connected to the controversial immigration bill Brewer signed into law last month.
Calls to Brewer's office seeking comment were not immediately returned on Friday.
Arizona Capitol Police Chief Andrew Staubitz told the Arizona Republic that lab results taken by Health Department officials confirmed that no employees were at risk during the Tuesday morning incident that shut down the Capitol Executive Tower for roughly 45 minutes.
The letter, which was addressed to Brewer, was opened by an employee in the governor's constituency services office and contained a powdery substance that spilled onto a computer. No injuries or illnesses were reported.
"It's hopefully an isolated incident," Staubitz told the Arizona Republic.
Under the terms of Arizona's new law, authorities there 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 border with Mexico. According to government estimates, roughly one-third of all illegal immigrants enter the U.S. via Arizona.