WASHINGTON — The Supreme Court on Monday took away one of the government's tools for prosecuting and deporting workers in this country illegally, ruling that the crime of identity theft was limited to those who knew they were using another person's Social Security number.
People who use false documents can be jailed, the court said. But they cannot be convicted of the more serious crime of "aggravated identity theft" without proof that they knew the identification number belonged to someone else, the court ruled unanimously.
The justices also set the stage for a ruling on long prison terms for juveniles. They voted to decide, in two cases from Florida, whether it was cruel and unusual punishment to impose a life term on a minor as young as 13 for a crime such as rape or murder.
And in an environmental cleanup case from California, the court said corporate polluters should pay for the contamination they caused, not the full cost of the cleanup.
The ruling on identity theft will probably boost the Obama administration's plan to target employers who knowingly hire illegal workers, rather than focusing on illegal workers.
Deportation is usually a slow process if the illegal immigrant does not have a serious felony on his record. But a conviction for aggravated identity theft would most likely lead to a speedy deportation.
Last year, the Bush administration announced roundups of illegal immigrants at several workplaces. Most of those arrested were charged with possessing false documents and aggravated identity theft. For example, 389 workers were detained at a meat-packing plant in Iowa; two-thirds of them were charged with felony identity theft.
The novel use of the law prompted the Supreme Court to take up the issue. Five years ago, Congress strengthened the penalties against thieves who stole identities and used the information to take money from people's bank accounts or charge expenses to them. It called for a mandatory two-year prison term for each offense.
But the court was told that fewer than half of all the possible nine-digit combinations had been used at some time for Social Security numbers.
And the law suggested the criminal had to intend to steal a person's identity. It referred to someone who "knowingly" uses the identification of another person.
The court said the provision did not cover an illegal worker with a phony Social Security card who did not know whether its numbers were those of an actual person.
Justice Stephen G. Breyer cited some common examples. "If we say that someone knowingly ate a sandwich with cheese, we normally assume that the person knew both that he was eating a sandwich and that it contained cheese," he said.
The decision in Flores-Figueroa vs. U.S. overturns part of an Illinois man's conviction for using false documents. Ignacio Flores-Figueroa, a citizen of Mexico, said he bought a set of false documents in Chicago and used them to work at a steel plant in East Moline, Ill.
The Florida cases on prison terms for juveniles will be heard in the fall.
In the past, the court has called the death penalty cruel and unusual punishment for some killers. In 2005, the court abolished executions for murderers who were under 18 at the time of their crimes.
But the justices have rarely, if ever, put constitutional limits on prison terms. The justices upheld California's "three strikes" law against a constitutional challenge, even when it resulted in a life prison term for a man whose third offense was a petty theft.
Still, the court has never ruled on extreme prison terms for such young offenders.
Joe Sullivan was 13 in 1989 when he was convicted and given a life term for his part in the burglary and rape of an elderly woman.
The court also agreed to hear an appeal from Terrance Graham, who was 17 when he pleaded guilty to armed home-invasion robberies in 2004. He also received a life term.
The court's environmental ruling will spare companies from paying the costs of a cleanup if they did no more than sell a dangerous chemical to another company.
Shell Oil Co. sold chemicals for many years to a now-defunct farm chemical company in Arvin, Calif., near Bakersfield. Chemicals got into the ground and contaminated the area.
After federal and state authorities moved in to clean up the site, they sought to hold all of the alleged polluters liable for the costs, including Shell and a railroad company that owned a small portion of the land.
They won before a federal judge and the U.S. 9th Circuit Court of Appeals but lost in the Supreme Court.
In a 8-1 decision, the justices said Shell was not liable for selling the chemicals. The law says a company that "arranged" for the dumping of hazardous chemicals can be forced to pay for the cleanup. But the justices said selling a chemical to another firm was not arranging for it to be dumped.
The justices also said Burlington Northern Railroad was liable for 9% of the cleanup cost because its role was minor.