An article in the Chronicle Wednesday (“Arizona law hanging over Calderon visit,” Page A7) erroneously said that Arizona's new law “allows police to stop and question anyone suspected of being in the country illegally.” This statement is flatly untrue. It's not even close to being true. And it's the kind of statement that does a disservice to people who are trying to make reasoned arguments either way about the Arizona law.

The Arizona law makes it clear that there must first be a valid “lawful stop, detention or arrest” before any investigation of immigration status can begin. The valid “stop, detention or arrest” cannot involve immigration status; it has to be independent, based upon an “other law or ordinance.” These are quotations from the text of the law.

A stop, detention or arrest can't be justified by merely suspecting someone's immigration status. It is only after a valid arrest, stop or detention has been established — only at that point — that a police officer can even consider investigating immigration status, under the Arizona law. And at that point, the officer still can't investigate, unless there are “reasonable” grounds to suspect illegal entry. And even then, he can only make a “reasonable effort ... to determine the person's immigration status.”

More importantly, the officer can't begin to make an arrest, unless the inquiry produces a solid basis, or in other words, probable cause for arrest. And the Arizona law says that ethnicity — a person's appearance — cannot be considered as the basis of the reasonable grounds. It doesn't have to say this, because it's already the law, but it's a good thing for Arizona to restate it explicitly.

As an example, consider the case of the Oklahoma City bomber, Timothy McVeigh. This terrorist was apprehended as the result of a routine traffic stop. The officer who stopped him didn't know McVeigh was a capital murderer. He had no license plates, and that is why he was pulled over. The traffic stop disclosed that McVeigh had no vehicle registration and was carrying a handgun without a permit. But the reason for McVeigh's apprehension certainly was not because he was “someone suspected of being a terrorist,” although that kind of reasoning might seem analogous to the erroneous statements about the law that have been made in the media.

It was only after he was detained in a valid, lawful traffic stop, based on independent grounds, after the facts prompted the police to undertake an investigation, that they developed evidence that McVeigh was the bomber who had killed more than a hundred people in a federal building. That's the way it should be done. And that's what the Arizona law does, in the case of immigration violations.

In fact, ordinary vehicle stops result in a large percentage of lawful arrests. For misdemeanors, felonies, and even capital crimes like McVeigh's. This is so because traffic violations frequently bring officers into positions to witness evidence of minor crimes or very serious crimes that they did not suspect when they signaled the vehicle to pull over. We ought to appreciate it when a police officer is alert and curious during a traffic stop. That's what the Arizona law is about. If an officer sees indications of a crime, he should ask questions and look for further evidence. That is what the police did in Timothy McVeigh's case, and it is what they should do in other cases when they have made a lawful arrest, stop, or detention. Including investigating immigration crimes. But that doesn't mean, as erroneously reported, that officers can “stop anyone suspected” of a crime, and the Arizona law doesn't authorize that at all.

Part of the opposition to the Arizona law comes from people who simply don't know what the law says. And that includes some people in high places.

A few days ago, under questioning by U.S. Rep. Ted Poe, R-Humble, the attorney general of the United States, Eric Holder, admitted that he hadn't read the Arizona law. That's amazing, since Holder had called for consideration of a lawsuit to declare unconstitutional the law he hadn't read.

And a part of the opposition to the Arizona law, I think, comes from people who don't want us to follow the rule of law in immigration matters. This includes so-called sanctuary cities such as San Francisco, whose officials have criticized the law.

There are legitimate questions about the Arizona law. Will it result in a tendency toward pretextual stops because officers are motivated to find immigration violations? I doubt it, but others are sure of it, and the answer is that it's speculation either way. We'll have to see how it works. Will individuals who are in the country illegally decline to report crimes, more so than they do now, as a result of the Arizona law? I doubt it, since a valid apprehension is required first, and since such people already are reluctant; but others are sure they know the opposite. And again, we'll have to find out.

Meanwhile, the media's erroneous characterization of the Arizona law doesn't help anyone answer these serious questions at all.

Crump is the John B. Neibel Professor of Law at the University of Houston Law Center.