The U.S. Justice Department filed a federal lawsuit against Maricopa County Sheriff Joe Arpaio, his office and the county on Thursday.

Maricopa County Sheriff Joe Arpaio responded to news of the Department of Justice's lawsuit at a press conference Thursday in Phoenix. (Photo by Al Macias)

The announcement came after negotiations between the DOJ and the sheriff's office broke down last month. The suit accuses Arpaio and the sheriff’s office of discriminatory and unconstitutional law enforcement practices.

DOJ said this is only the second time in its 18 years of civil police reform work that it has had to file a contested lawsuit. Assistant Attorney General for Civil Rights Tom Perez says all of the allegations in the complaint result from a culture of disregard for basic human rights within the agency -- and he says that starts at the top.

“At its core, this is an abuse of power case, involving a sheriff and a sheriff’s office that disregarded the Constitution, ignored sound police practices, compromised public safety and did not hesitate to retaliate against perceived critics,” Perez said.

Perez said he still hopes to reach a settlement with Arpaio’s office. Any agreement, though, would require Arpaio to allow an independent monitor in his office. He has so far refused to do that.

The sheriff says he's not backing down and welcomes a trial.

"It's the monitor plus DOJ that would have veto power over the sheriff," said Joseph Popolizio, one of the attorneys representing the Arpaio. "For in stance if the sheriff, under this agreement as they proposed, went to the monitor and the Department of Justice and said 'I want to implement this new process or policy or procedure,' they would have veto power."

Assistant Attorney General for Civil Rights Thomas E. Perez with Deputy Assistant Attorney General Roy Austin. (Photo by Mark Brodie - KJZZ)

Latino community leaders in Phoenix said the DOJ's civil lawsuit came as no surprise. Maricopa County supervisor Mary Rose Wilcox, an Arpaio critic and target of retaliation by the sheriff and county attorney, said the legal proceedings could cause problems for the entire county.

"All of the things here violate the United States Constitution, so the county not only stands to have to spend money for compliance -- if that is what we have to do for lawyers -- but we also may lose our federal funding," Wilcox said.

Wilcox said it could take months or years for the lawsuit to settle. That would be enough time for more people to come forward with additional claims against Maricopa County.

Arpaio said again the investigation is politically motivated by the Obama administration. He said the timing of the suit during an election year was intentional.

He also denied that Wednesday's release of a handbook with new policies and procedures for the sheriff's department was motivated by the DOJ's lawsuit announcement.

"We've been working on that for a long time," Arpaio said. "At least six weeks. But we've been accumulating information. I think that was a nice document; the reason we did that was to show the public we are a good law enforcement agency."

Read the Department of Justice complaint filed Thursday.

Mark Brodie, Nadine Arroyo Rodriguez and Al Macias contributed to this report.

Updated 05/10/2012 at 7:29 p.m.