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A Colorado county judge says that tax records belonging to undocumented immigrants who were investigated for alleged identity theft must be destroyed because they should not have been seized in the first place.

The Weld County judge's order followed a ruling by the state Supreme Court that said investigators illegally probed suspected identity theft by illegal immigrants.

The high court had already halted the investigation led by District Attorney Ken Buck by ruling it was illegal, but the lower court's order this week makes permanent an injunction in the case.

The investigation marked the first time in the U.S. that authorities tried to use tax returns, which are confidential under federal law, to prosecute suspected illegal immigrants.

Weld County District Judge Stephen J. Schapanski on Tuesday ordered that the thousands of tax documents seized from a Greeley tax preparer be destroyed, and the judge barred authorities from using any of the information they gathered for any prosecutions.

The documents were handed over to a court clerk when the preliminary injunction was entered in April 2009. Eight months later, the Supreme Court ruled the investigation violated the constitutional and privacy rights of suspected illegal immigrants.

Buck, a Republican who narrowly lost to Democrat Michael Bennet in Colorado's U.S. Senate race, did not immediately return a call left at his office for comment. In the past, he defended his investigation, dubbed "Operation Numbers Game," saying he was trying to address a serious identity theft problem in the county.

Buck and sheriff's investigators alleged that up to 1,300 immigrants were filing tax returns using false or stolen identities. All the tax documents that were seized came from Amalia's Translation and Tax Service, a business that catered to Hispanics.

The American Civil Liberties Union filed suit, saying the investigation violated federal privacy laws. Buck argued the seizures didn't violate the law because the records were not obtained from the Internal Revenue Service and because they were part of a criminal investigation.

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