( CNN ) -- An Arizona lawman said the suspicious package addressed to controversial Sheriff Joe Arpaio `` would have caused a major explosion '' if someone had opened it . Jerry Sheridan , chief deputy of the Maricopa County Sheriff 's Department , told reporters Friday the package was noticed by an alert postal employee in Flagstaff who thought he spotted gunpowder residue . Arpaio was at Sheridan 's side as he spoke . Police in Flagstaff X-rayed the package , noticed what appeared to be an explosive device , and rendered it safe by blowing it up with a water cannon . Sheridan said the package was mailed Thursday , a day after the department received a death threat from a major drug cartel . The department has received other threats in the past , but , Sheridan said , this development is `` something that was brought to the height of seriousness . '' `` That is a very serious threat . It was labeled to come here , to this building and to be opened by Sheriff Arpaio , '' Sheridan said . He said injuries , burns and maybe death could have resulted . The FBI and deputies were trying to track down `` a person of interest . '' Arpaio , well-known for his hardline anti-immigration policies that have led to accusations of civil rights violations , vowed that he would not be brought down by his enemies . He spoke after Sheridan briefed reporters . He said he 's been besieged by certain groups and people and has been slammed with rhetoric criticizing him . He said he 's resolved to do his job and wo n't be intimidated by people who want to force him out of office or kill him . `` My answer is it will not deter me from doing my job , '' he said . `` I 'm not running scared . `` All I know is I 'm going to keep being the sheriff , '' he added . `` I want everybody to know that . '' Earlier , sheriff 's department spokeswoman Lisa Allen said it was her understanding that the package had gun powder , wires , a battery -- all the components for an explosion . U.S . Postal Inspector Andrew Rivas in Flagstaff , who screened the package Thursday , considered it suspicious enough to call a local police bomb squad and the FBI . `` We evacuated the post office , got all our employees to safety , '' Rivas told CNN affiliate KTVK . Rivas said authorities have an idea of where the package may have come from , but declined to specify , citing the ongoing investigation . Allen said the origin of the package is one of the underlying issues in the investigation . At present , the department is not opening mail and is checking to see if any suspicious packages have made it through , Allen said . Neither she nor Flagstaff police knew if the box contained a message . The FBI declined to release details . `` I can confirm the FBI is involved in the investigation , '' said FBI spokesman Manuel Johnson in Phoenix . `` At this time the FBI is not commenting further due to the matter being ongoing . '' The Bureau of Alcohol , Tobacco , Firearms and Explosives also is investigating , ATF spokesman Mike Campbell said . Flagstaff is about 150 miles north of Phoenix , the seat of Maricopa County . A lightning rod for controversy . Arpaio has made national headlines for years with his unorthodox -- and often controversial -- style of justice . And he has been the object of threats before . Since August 2011 , nine threats have been directed at Arpaio that were were credible enough to be investigated . There has been at least one arrest in the past involving threats . While Arpaio already has reasonable security , Allen said , `` we are going to have to augment '' it either by getting more personnel or adding electronic security . Arpaio has housed thousands of inmates in tents and forced all inmates to wear pink underwear . He has boasted about feeding each inmate on less than $ 1 a day . His critics say he has a long history of launching bogus criminal investigations against political opponents and anyone else who gets in his way . He was the subject of a civil lawsuit by the Justice Department alleging civil rights violations . According to the complaint , the sheriff 's office has displayed a pattern of discrimination against Latinos that includes racial profiling , unlawful detention and searches , and unlawful targeting of Latinos during raids . Arpaio has denied any discrimination , and one of his attorneys called the Justice Department investigation a `` witch hunt . '' His office website touts his `` get tough '' policies and says his chain gangs contribute thousands of dollars of free labor to the community . Male chain gangs , as well as the world 's first-ever female and juvenile chain gangs , clean streets , paint over graffiti and bury the indigent in the county cemetery . After winning his sixth term last November , the 80-year-old sheriff said he does n't plan on leaving office anytime soon . `` For my critics out there , I 'm going to say right now : In January , I 'm signing up for 2016 . So I 'm not a lame duck , '' he told a crowd of cheering supporters . CNN 's Greg Morrison , Ashley Fantz and Michael Martinez contributed to this report .
NEW : ` ` All I know is I ' m going to keep being the sheriff , '' Arpaio says . Maricopa County Sheriff Joe Arpaio has staunch supporters and fierce critics . His anti - immigration policies have led to accusations of civil rights violations . Arpaio won his sixth term in November and told supporters he will run again in 2016 .