A postal carrier collected the suspicious package Thursday evening from a parcel locker in rural Coconino County, near Flagstaff, Ariz., which was addressed to Arpaio at his office in downtown Phoenix, said Jerry Sheridan, chief deputy of the Maricopa County Sheriff's Office, at a news conference Friday.
The carrier brought the package to the Flagstaff post office, where postal officials X-rayed it and found an improvised explosive device. The Flagstaff Police Department bomb squad used a water cannon to neutralize the explosives, said US Postal Inspection Service spokesman Keith Moore.
Arpaio told reporters that this is not the first time he has been threatened.
"Of course you worry. I'm a victim, I'm a witness,” he said. “When you convict people, the victim has to be somewhat concerned. I'm a little concerned about my family. I didn't ask for all these threats."
Sheridan said the Maricopa County Sheriff’s Office had endured “years of threats” against Arpaio, including $4 million bounties on his head, but the bomb package raised the threats to a new "height of seriousness."
“What evidence we have indicates that had someone opened that package, it would have created a major explosion and caused serious physical injury, burns, and maybe death,” Sheridan said. “That is a very serious threat.”
Arpaio said he receives many packages, some of which he opens personally. The person who sent this package would be brought to justice, he said.
"I'm not going to be intimidated by anyone, that's a promise," he said.
Arpaio won his sixth election as sheriff of Arizona’s most populous county last November, but his office is not without controversy.
His unconventional law-enforcement methods – including dressing inmates in pink underwear – and strong stance against illegal immigration have brought Arpaio national attention, the Monitor reported last year. According to the Associated Press, he has cost the county $25 million in legal settlements over inmate treatment in county jails. His critics also charge that his office has failed to investigate more than 400 sex-crime cases and that the deputies racially profile Latinos in traffic patrols.
He created headlines in January when he created a posse of armed volunteers to patrol near schools in the Phoenix area to strengthen school security.
Initial reports about the package indicate it may have been damaged during transport and leaked gunpowder, Tom Mangan, Phoenix spokesman for the Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF), told the Associated Press.
The Federal Bureau of Investigation, ATF, and threat detectives for the Maricopa County Sheriff’s Office are assisting the Flagstaff postal inspector, who is the primary investigator in the case, Sheridan said.
Andrew Rivas, the postal inspector, screened the package Thursday and called the police and FBI.
“We evacuated the post office, got all our employees to safety," Mr. Rivas told CNN.
Authorities have a lead on where the package may have come from, Rivas said, but he declined to specify because of the ongoing investigation.
The office is not opening mail and is checking for other suspicious packages, said sheriff’s department spokeswoman Lisa Allen, according to CNN.
• Material from the Associated Press was used in this report.