Maricopa County Chief Deputy Jerry Sheridan made the comment Friday at a news conference in Phoenix. He said investigators are trying to locate one person who may have been involved in mailing the package addressed to his boss.
The package intercepted late Thursday was addressed to Arpaio at his downtown Phoenix office. It had been left in a parcel locker that was part of a multiple address mailbox in a rural part of Coconino County, outside Flagstaff city limits.
U.S. Postal Inspection Service spokesman Keith Moore said a courier called his supervisor after noting it was suspicious, and the package was eventually brought into the main Post Office in Flagstaff. An X-Ray showed what appeared to be bomb-like components, including wires and a container, and authorities used a water cannon to neutralize the package, Sheridan said.
Arpaio, the self-proclaimed "toughest sheriff in America," said this isn't the first time he's been threatened. Arpaio is known nationally for his strict treatment of jail inmates and cracking down on illegal immigration.
"Of course you worry. I'm a victim, I'm a witness. When you convict people, the victim has to be somewhat concerned.
Postal Inspector Patricia Armstrong said authorities were alerted by a "very astute" carrier who observed "something suspicious" about the package.
Armstrong didn't elaborate on what raised suspicion, but Tom Mangan, a spokesman in Phoenix for the federal Bureau of Alcohol, Tobacco, Firearms and Explosives, said initial reports indicated that the package was a box that might have been damaged in transit and leaked gunpowder.
Sheridan said the package contained black powder and an ignition device, although he wasn't sure if it was packed into a container and would have exploded or simply ignited in a flash fire. Either way, he said, it was very dangerous.
"Had someone opened that package, it would have caused a major explosion and caused serious physical injury, burns and maybe death," Sheridan said. "That is a very, very serious threat."
Authorities in Flagstaff, which is about 140 miles north of Phoenix, said they are pursuing leads in the case.
Arpaio said he receives lots of packages, including ones with cookies recently as he recuperated from a broken shoulder suffered when he fell crossing a street on his way to lunch. He said he opens some of the packages personally.
"Hey, they send me cookies, now they send me bombs," he said Friday. "It's a little different."
Arpaio said the mailing of an explosive device addressed to him comes with his line of work. He cited the recent killings of a West Virginia sheriff, Colorado's corrections director and two prosecutors in Texas.
"That's the nature of the business," he said.
Arpaio said whoever is responsible for mailing the package, if found, would be brought to justice.
"I'm not going to be intimidated by anyone, that's a promise," he said.
Following the killing of a West Virginia sheriff last week, Arpaio said elected law enforcement officials across the nation seem to be targeted.
Arpaio has had a security detail for years, and regularly receives threats. This week, the sheriff's office said he had received threats from Mexican drug cartels which put a $4 million bounty on him and possibly dispatched a hit man to attack him.
The office distributed a list of 10 cases since mid-2011 where people threatened the sheriff, who is known for housing inmates in tents and forcing the men to wear pink underwear. Most involved people posting threats on the Internet or following routine arrests. Several suffered from a mental illness, and several people reportedly were prompted by Arpaio's stance against illegal immigrations.
Sheridan said there's no evidence linking the package found Thursday with a specific threat or cartels.
A campaign to recall Arpaio began just weeks after he started his sixth term in January.
Critics contend that Arpaio should be ousted because his office failed to adequately investigate more than 400 sex-crimes cases, allegedly racially profiled Latinos in its trademark immigration patrols and has cost the county $25 million in legal settlements over treatment in county jails.
Arpaio has denied that his deputies racially profiled Latinos in traffic patrols targeting illegal immigration. His office has moved to clear up the sex-crime cases and moved to prevent the problem from happening again, he said.
Sheridan and Arpaio both lashed out at the Department of Justice and immigrant activists who criticize him, saying they rile up people who are unstable and end up threatening Arpaio.
"I'm saying the tempo out there, about this sheriff, does cause people to do bad things," Arpaio said.
Fonseca reported from Flagstaff, Ariz. Associated Press Writer Paul Davenport in Phoenix also contributed to this report.