One of the subtle things that help explain why the United States is a great country is that a prosecutor has ethical responsibilities that go beyond those of a defense attorney. A prosecutor's duty -- like that of a police officer -- is to seek justice.

Unfortunately, police and prosecutors now seem to commonly believe that executing a defendant is so important that it justifies acting unethically -- e.g., by leaking information with the intention of prejudicing potential jurors.

In the past few weeks, anonymous law enforcement personnel have leaked stories to The Post claiming that John Lee Malvo, the 17-year-old sniper suspect, has confessed to being the shooter in several of the spree murders [front page, Nov. 10 and 11]. Even if the confession turns out to be inaccurate, jurors will "know" that Malvo confessed to murder.

Malvo's prosecutor, Fairfax County Commonwealth's Attorney Robert F. Horan Jr., said he was "as outraged as the defense attorneys" that statements were leaked that could harm the defendant's right to a fair trial. But he then added that because leaking was not a prosecutable offense, "unfortunately they [the police] can do it if they want to."

That is not an ethical approach to law enforcement, and it helps explain why such abuses are common. Prosecutors like Horan are failing to exercise ethical management.

A prosecutor or a police chief can fire employees who leak confidential information for the purpose of harming someone's constitutional rights: In other words, press leaks stop when the top cop and prosecutor want them to stop. Moreover, if prosecutors and police chiefs in Virginia were to ask for a law making such leaks a crime, it likely would be passed promptly.

Why has Virginia failed to adopt such a law, despite years of abuses?

The articles on Malvo make that clear. The first problem is proving that the government is responsible for the leaks. The second problem is that even if it can be proven that the government was the source of the leaks, the courts are reluctant to overturn a conviction. The result is that governmental "crime" pays. Leaks are common because they work, and because they are not punished.

In the end, the issue is ethics. Prosecutors and police want convictions. Only a sense of ethics and public responsibility can make them rise above that self-interest and return to their core duty -- seeking justice.

-- William K. Black

is a lawyer, a criminologist and an assistant professor at the LBJ School of Public Affairs of the University of Texas at Austin.