Caballes was wearing a suit and driving a new Mercury when he was stopped on an Illinois freeway in November 1998. It looked like he would get off with a warning until Krott the drug dog showed up and sniffed out $250,000 worth of marijuana in Caballes' trunk.
Caballes' conviction eventually was overturned on grounds police had no reason to search his car.
Dogs trained to find drugs and bombs are becoming more common in airports and elsewhere — even the Supreme Court — because of terrorism concerns. Police also often use them for routine traffic stops.
Justices will decide whether people who have given police no reason to suspect illegal activity have a constitutional protection against dog searches.
The Supreme Court has tried in recent years to better define someone's right to be left alone in their homes and vehicles. In this case, the court must clarify earlier opinions that found that drug dog use is not necessarily a search that falls under the Fourth Amendment ban on unreasonable searches or seizures.
"A sniff is not a search," justices were told by Illinois Attorney General Lisa Madigan.
Chicago attorney Ralph Meczyk, representing Caballes, countered. "It is accusatory. It is profoundly embarrassing."
Justice David Souter appeared troubled by the prospect of more use of dogs.
"We're opening a large vista for dog intrusion," said Souter, adding that he was worried about officers canvassing garages and neighborhoods with animals. Police "can take a dog to a front door and ring the bell and see what happens."
Justice Ruth Bader Ginsburg, a petite 71-year-old, said "dogs can be frightening, humiliating."
Madigan responded that millions of people have dogs as pets.
Christopher Wray, a Bush administration lawyer who joined Madigan to defend dog searches, noted that beagles — generally seen as unimposing — are used in airports to detect illegal vegetables and other canines have a long history in crime-fighting.
Several justices, including key swing voters on civil liberties cases, seemed reluctant to restrain police.
Justice Stephen Breyer said police officers can sniff for contraband during a traffic stop, why not a dog? It's a fact of life, he said, "you might run into people and animals with sharp noses."
Justice Antonin Scalia said drug dogs have been around a long time and "the Republic seems to have survived." And Justice Sandra Day O'Connor said that canines just sniff around cars, not inside them.
However, Justice John Paul Stevens said an opening for dog searches in run-of-the-mill situations would also allow the use of mechanical devices to search people.
Caballes was pulled over for driving 71 mph on a stretch of Interstate 80 with a 65 mph limit. Caballes said he was moving from Las Vegas to Chicago because his girlfriend had broken up with him. The state trooper noticed air freshener in the car and asked for permission to search Caballes' trunk. Caballes refused, but officers searched it later anyway after the dog indicated there were drugs in the trunk.
His conviction for drug trafficking was thrown out by the Illinois Supreme Court. Illinois was supported by 28 states and several law enforcement groups in its appeal to the high court.
The argument inspired many canine jokes. Caballes' lawyer at one point asked if he was an underdog in the case.
The case is Illinois v. Caballes, 03-923.