PHOENIX (By Eduardo Montes, AP) March 11, 2009 — Federal authorities told a high-profile Arizona sheriff Tuesday that they will investigate his department over allegations of discrimination and unconstitutional searches and seizures.

The U.S. Justice Department said in a letter to Maricopa County Sheriff Joe Arpaio that investigators will focus on alleged patterns of police discrimination based on national origin.

The letter offers no specific allegations. But Arpaio said he believes the investigation was spurred by his department's often controversial efforts to combat illegal immigration in Maricopa County, which includes Phoenix.

Arpaio's department is the largest participant in a federal program that allows local police departments to enforce federal immigration laws.

The department has aggressively pursued investigations under Arizona's employer sanctions law and a state anti-smuggling law.

The smuggling law was designed to help local police fight smugglers, but an interpretation by Maricopa County's top prosecutor opened the door for Arpaio's deputies to arrest people who pay smugglers and accuse them of being co-conspirators.

Arpaio has also launched crime sweeps in areas around Phoenix with high concentrations of Hispanics. Most recently, Arpaio began to separate illegal immigrants from other inmates in Tent City, a section of the county jail where all inmates are housed in tents.

Those tactics have attracted national attention and have led some critics, including immigration activists, to accuse Arpaio's department of racial profiling.

The sheriff said he will cooperate with the Justice Department. "If they want to come down, let them come," he said. "We'll open our books. We have nothing to hide."