The government can prosecute and imprison people for crimes based on evidence obtained from their computers—even evidence retained for years that was outside the scope of an original probable-cause search warrant, a US federal appeals court has said in a 100-page opinion paired with a blistering dissent.

The 2nd US Circuit Court of Appeals ruled that there was no constitutional violation because the authorities acted in good faith when they initially obtained a search warrant, held on to the files for years, and built a case unrelated to the original search.

The case posed a vexing question—how long may the authorities keep somebody's computer files that were obtained during a search but were not germane to that search? The convicted accountant said that only the computer files pertaining to his client—who was being investigated as part of an Army overbilling scandal—should have been retained by the government during a 2003 search. All of his personal files, which eventually led to his own tax-evasion conviction, should have been purged, he argued.

But the appeals court said the authorities' behavior was acceptable and didn't reach the constitutional question of whether the Fourth Amendment rights were breached for accountant Stavros Ganias, who was sentenced to two years in prison. That's because three years after the original search of the accountant's files in connection to the Army scandal, Connecticut authorities got another search warrant for Ganias' own tax files that were already in the government's possession, the appeals court ruled in a 12-1 decision Friday written by Judges Debra Ann Livingston and Gerard Lynch. Ganias had subsequently deleted those files from his hard drives after the government had imaged them, according to court records:

Defendant-Appellant Stavros Ganias appeals from a judgment of the United States District Court for the District of Connecticut (Thompson, J.) convicting him, after a jury trial, of two counts of tax evasion in violation of 26 U.S.C. § 7201. He challenges his conviction on the ground that the Government violated his Fourth Amendment rights when, after lawfully copying three of his hard drives for off-site review pursuant to a 2003 search warrant, it retained these full forensic copies (or “mirrors”), which included data both responsive and non-responsive to the 2003 warrant, while its investigation continued, and ultimately searched the non-responsive data pursuant to a second warrant in 2006. Ganias contends that the Government had successfully sorted the data on the mirrors responsive to the 2003 warrant from the non-responsive data by January 2005, and that the retention of the mirrors thereafter (and, by extension, the 2006 search, which would not have been possible but for that retention) violated the Fourth Amendment. He argues that evidence obtained in executing the 2006 search warrant should therefore have been suppressed. We conclude that the Government relied in good faith on the 2006 warrant, and that this reliance was objectively reasonable. Accordingly, we need not decide whether retention of the forensic mirrors violated the Fourth Amendment, and we AFFIRM the judgment of the district court.

The case is clearly nuanced, but it has huge ramifications for the public because many people keep all of their papers and effects co-mingled on their hard drives.

In his 40-page dissent, Judge Denny Chin blasted the majority opinion and said the authorities wrongly seized files from Ganias that were unrelated to the Army overbilling investigation. "The government did precisely what the Fourth Amendment forbids: it entered Ganias' premises with a warrant to seize certain papers and indiscriminately seized—and retained—all papers instead," Chin wrote.

This is not the first time the appeals court entertained the case. Last year, the court sided (PDF) with Ganias in a 2-1 ruling. But the government asked for the full appeals court to rehear the case en banc, and the court agreed to do so with all 13 judges. The court's original ruling for Ganias said investigators had a right to image Ganias' three hard drives at the center of the Army overbilling dispute. But the majority concluded that the law did not allow "officials executing a warrant for the seizure of particular data on a computer to seize and indefinitely retain every file on a computer for use in future criminal proceedings."

Ganias' lawyer, Stanley Twardy, urged the government to set aside his client's conviction.

"The seizure and two-and-a-half year retention of every file on Ganias' computers violated the Fourth Amendment," Twardy wrote. (PDF) He told the New York-based appeals court that "at a minimum the Fourth Amendment requires prompt completion of an off-site review and return of files outside the warrant's scope."

The government countered, "Consistent with the Fourth Amendment, the government may obtain a search warrant for nearly any person, place, or thing if the government establishes probable cause for the search and did not engage in an illegal seizure of the item to be searched," Assistant US Attorney Sandra Glover wrote in the government's filing. (PDF)