Maricopa County Sheriff Joe Arpaio's office said it will not open any more mail received at its headquarters until further notice.
An email from the sheriff's office said the decision was due, in part, to the fact that "Sheriff Arpaio is a recently targeted recipient of an explosive device."
The announcement Wednesday morning came after emergency response crews reported to a hazardous materials call after a staff at U.S. Sen. Jeff Flake's office in Phoenix reported two suspicious envelopes.
President Barack Obama and a Mississippi senator recently received packages that preliminarily tested positive for ricin, a potentially deadly poisonous chemical.
A package containing an explosive device and addressed to Arpaio was intercepted April 11 near Flagstaff.
Officials said the package would have exploded if opened, leading to serious injuries or death.
It had been left in a parcel locker in a rural part of Coconino County, outside the Flagstaff city limits. U.S. Postal Inspection Service spokesman Keith Moore said a courier brought it into the main Post Office in Flagstaff. It was X-rayed and the device was detected. A bomb squad used a water cannon to neutralize the package.
The Maricopa County Sheriff's Office held a news conference late Friday morning. A MCSO spokesperson said they have learned that had someone opened the package, it would have exploded and could have caused serious injury, or death, according to MCSO.
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