GREELEY — The Colorado Supreme Court ruled Monday that a 2008 raid of a local tax preparer’s office aimed at building identity-theft cases against hundreds of suspected illegal immigrants violated their Fourth Amendment right to privacy.

The 4-3 ruling was the latest and most devastating legal blow against Operation Numbers Game, an investigation launched by Weld County Sheriff John Cooke and District Attorney Ken Buck that aimed to use tax returns to identify and prosecute illegal immigrants.

The raid on Amalia’s Tax and Translation, a business that caters to Spanish-speaking clients, led to the seizure and review of some 4,900 tax returns. Deputies said they found about 1,300 suspects in identity-theft and criminal-impersonation cases.

More than 100 suspected illegal immigrants were arrested because of the raid, and charges were formally filed against 70 of them. About 60 cases were then dismissed after Weld District Judge James Hartmann, ruling in one of the criminal cases, tossed evidence investigators had seized during their search of Amalia’s.

No more than three of the criminal cases made it to Colorado’s high court, including the case in which the justices ruled Monday, said Mark Silverstein, American Civil Liberties Union legal director.

On Monday, Buck conceded Operation Numbers Game “is over,” adding he will not appeal the decision. A Colorado prosecutor can appeal a case only as far as the state high court, according to Colorado law, but a defendant can appeal to a higher court.

But Buck felt the raid was justified.

“I feel the court made its decision and then later developed rationale for this decision,” Buck said.

Prosecutors around the country have been watching the case closely, reportedly the first in the United States in which law enforcement sought to use tax returns — generally considered confidential under federal law — to take suspected illegal immigrants to criminal court.

The court majority ruled that the defendant in this case, Ramon Gutierrez, as a taxpayer “has a reasonable expectation of privacy in his or her tax returns and return information, even when that information is in the custody of a tax preparer.”

The ruling also said that Gutierrez, who was among more than 70 people charged with criminal impersonation and identity theft, was a victim of an “exploratory search” and that police had no probable cause to search Gutierrez’s tax records.

Gutierrez has been free on bond and likely will have charges dismissed soon, Buck said.

Three justices dissented to the opinion.

Justice Nancy C. Rice wrote a dissent in which she said because police officers “acted in good faith when they seized the tax records, I find it unnecessary to consider whether the affidavit supporting the warrant failed to establish probable cause.” She was joined by Justice Allison Eid.

Justice Nathan B. Coats also wrote a dissent, in which he worried about bigger issues in the case, significantly the presumption that the tax preparers were shielded from criminal liability as they aided “taxpayers to knowingly report income earned under Social Security numbers belonging to someone else.”

“I believe it is a mistake that fundamentally distorts the majority’s Fourth Amendment analysis,” Coats wrote.

Kevin Strobel, the head of the Greeley public defender’s office, said police and prosecutors still have to follow the law when dealing with illegal immigrants.

“There’s still a constitutional framework for how authorities deal with that population and whether they’ve committed crimes or not,” Strobel said. “They gotta follow the rules.”

The court noted that four district judges have now ruled against Operation Numbers Game, including in a civil case against Buck and Cooke brought by the American Civil Liberties Union.

Buck said he didn’t know how the court’s Monday decision would affect his civil case. Tax returns in that case remain with the Weld County courts, pending a final Supreme Court decision.

Buck said he won’t be scared off from continuing to prosecute allegedly illegal immigrants.

“We were successful in a lot of different ways,” he said. “We showed there was an issue of a failed federal policy on illegal immigration, and people now understand the source of identity theft.

“And we gained valuable intelligence in fighting identity theft,” he said.

The Associated Press contributed to this report.

Monte Whaley: 720-929-0907 or mwhaley@denverpost.com