(CNN) - An unidentified person made two phone calls in which he threatened to blow up Rep. Raul Grijalva's Tucson, Arizona office and kill the congressman and his staff members, prompting the Democratic lawmaker to close his two district offices late Friday morning local time.
"It was the same guy," Grijalva's communications director Adam Sarvana told CNN. "He threatened to blow everyone's brains out in the Tucson office."
Grijalva arrived in his district from Washington Thursday night and was in the office at the time the second call came through.
The caller also said he was going to be "exercising my civil liberties and I'm shooting Mexicans at the border," according to Ruben Reyes, Grijalva's district director, who fielded one of the calls.
Reyes said tensions are running high in the state as a Saturday deadline nears for Arizona Gov. Jan Brewer to decide to either sign or veto a controversial immigration bill that would require police to question people if there's reason to suspect they're in the United States illegally. Grijalva urged Brewer to veto the legislation.
Sgt. Fabian Pacheco of the Tucson police department told CNN that the department was cooperating with federal and state authorities.
"We have some promising leads," he said, noting that the calls were made from a cell phone with a Phoenix area code.
Sarvana said both of Grijalva's district offices, in Tucson and Yuma, Arizona, would reopen on Monday morning.