PHOENIX -- Bomb-sniffing dogs hit on a suspicious package inside the sheriff's new headquarters Wednesday morning.
The building, which is still under construction, is located at Sixth Avenue and Jackson Street.
"Preliminary information is that police have found written communication on the building that there is a bomb planted somewhere inside the construction site," according to MCSO spokesman Brandon Jones.
Video and photos from the scene showed the phrases "Bomb inside," "No work today" and "Happy May Day" spray painted on an outside wall. Another message said, "Stop building prisons for other workers."
The building was evacuated and the bomb squad, including bomb-sniffing dogs, was brought in.
"Any threat we're going to take seriously," Jones said. "Our bomb dogs searched the entire building and, unfortunately, did hit on a suspicious package up on the second floor. It appears to be a lunchbox of some type."
The explosive ordnance team was called in to X-ray the item and handle it appropriately. Crews determined there were no explosives. The lunchbox contained only safety glasses and water. The scene was cleared by 9 a.m.
Construction crews were sent home for the day, but will resume work Thursday.
This is the second bomb threat directed at the headquarters of Maricopa County Sheriff Joe Arpaio in less than a month.
A couple of weeks ago, a package containing an explosive device was mailed to Arpaio at his downtown Phoenix office. That package was intercepted in Flagstaff.
"Officials say that bomb was made in such a way that had the package been opened, serious injury or death would likely have resulted," Jones wrote in an email to media outlets.
Investigators are trying to determine who sent that package.
Jones said it's not clear if Wednesday's threat is connected to that package.
"It is weird, kind of weird, if you will, or curious to us why both headquarters would have been targeted with any type of a bomb," he said.
"It's sad, but it looks like we're under attack," Arpaio told 3TV's Scott Pasmore and Kaley O'Kelley in a phone interview. "I don't know if there's any connection [between the two incidents] but we have to take these situations serious.
"I worry more about my employees," the sheriff continued. "I don't want anything to happen to my employees. If they want to go after someone, go after me, be my guest. I worry about the employees and public safety. Bombs are very dangerous."
Arpaio said threats like this will not scare him away and that he fully intends to run again in 2016.
"I'm not ready to retire yet," he said.
Arpaio and his department are scheduled to move into the new headquarters building in November.
May Day, which is also International Workers' Day, is generally associated with the workers' movement and often sees a variety of demonstrations in support of labor rights.