A suspicious package sent to the controversial anti-immigration Sheriff Joe Arpaio in Flagstaff, Arizona was found to contain explosive materials, police told KPNX and the Arizona Republic on Thursday evening.

An explosive test of the package revealed black powder, according to a spokesperson for the Bureau of Alcohol, Tobacco, Firearms and Explosives. The package was detonated with a water cannon and no one was injured in the process. An investigation into the origins of the package, which was picked up at a rural post office box, is underway.

"We’ve had suspicious packages with powder in them, but they turned out to not be anything," the sheriff’s Chief Deputy Jerry Sheridan said. "This was one was a real explosive devices. It could have seriously injured someone, had they opened it."

Arpaio has received numerous threats over the 20 years he's held office, some of which turned out to be hoaxes. In 1999, a bomb squad destroyed a spider sculpture outside Arpaio's Scottsdale home.

The sheriff's office said Arpaio often delays releasing information about public appearances until the last minute to minimize threats. Last week, Arpaio told the Arizona Republic that it was "very disheartening what’s going on with the elected officials (around the nation), and I hope they catch those perpetrators. We have to take precautions. I don’t expect any (security) increase, but it’s up to them (the security detail). It doesn’t bother me, but you still have to be concerned when you have all these threats."

Over the years, Arpaio has become nationally known for his extreme anti-immigration stance, endorsing Arizona's harsh immigration enforcement policies -- some of which have been thrown out by the Supreme Court because Arizona attempted to wrestle the authority to enforce immigration policy from the federal government. Arpaio is currently subject to a recall campaign, and proponents of the campaign say Arpaio has failed to investigate sex abuse crimes in El Mirage, which falls within Arpaio's jurisdiction.

Recently, one of Arpaio's legislative allies has introduced controversial legislation to curtail the effort.

Watch the video report, broadcast by KPNX on April 11.