In April 2002, a patient asked Virginia pain doctor William Hurwitz to write her a new prescription for methadone because her dog had eaten the original. Since this patient was arrested on drug charges four months later, her timeworn excuse looks like an obvious "red flag," one of many federal prosecutors would fault Hurwitz for ignoring.

Yet as the former owner of a sweet but destructive Labrador retriever, I can testify that dogs do sometimes shred and chew up valuable items. When that happens to a prescription for much-needed pain medication, what should a legitimate patient do? The government's answer, which Hurwitz could not in good conscience accept, can be summed up in one word: suffer.

By prosecuting Hurwitz for drug trafficking because some of his patients abused or sold painkillers he prescribed, the Justice Department reminded physicians throughout the country that they are expected to be cops as well as doctors. If they fail to reconcile these irreconcilable roles, if they do not treat their patients like criminals as well as customers, they can be convicted of felonies punishable by decades in prison, as Hurwitz recently was.

Hurwitz was a bad cop. He believed his patients when they said they were in pain. He gave them the benefit of the doubt when they asked for early refills, which could indicate diversion but also could indicate inadequate doses. He continued treating their pain after they tested positive for cocaine. He hesitated to abandon problem patients he knew would have trouble getting treatment elsewhere.

The qualities that made Hurwitz a bad cop also made him a compassionate doctor, the sort you would want treating you if you suffered from unrelenting chronic pain and needed large doses of narcotics simply to live a halfway normal life. Because few doctors are willing to accept the legal jeopardy associated with treating such patients, Hurwitz's clinic attracted hundreds from around the country.

After Hurwitz's practice was shut down in 2002, two of his patients killed themselves because they could not get adequate pain relief anywhere else. In the face of such desperation, Hurwitz's conviction sends exactly the wrong message, telling doctors they risk their liberty as well as their licenses and livelihoods if they place their patients' interests above the government's demand that they help fight the war on drugs.

The Hurwitz case shows it's not just "pill mill" operators who need to worry. The jury, which convicted him on 16 out of 45 counts and acquitted him on 17 (the judge dismissed the rest), did not seem to accept the government's portrayal of him as a drug dealer in a white coat.

In interviews with New York Times science columnist John Tierney, three jurors conceded that Hurwitz, who received no money from black-market drug sales, appeared to be a sincere physician who was hoodwinked by unscrupulous patients. "These patients used the doctor shamelessly," said one juror. "I don't see him getting anything financial out of it. Many of the patients weren't even paying him. He had to believe that he was just treating them for pain."

This was the very issue that last year led the U.S. Court of Appeals for the 4th Circuit to overturn the 25-year prison sentence that resulted from Hurwitz's first drug trafficking trial. The prosecution said it did not matter whether Hurwitz was acting in good faith, and the appeals court disagreed.

"There were just some times he fell down on the job," a juror told Tierney. Which job? Some critics have accused Hurwitz of bad medical judgment, to which the proper legal response is civil liability or regulatory sanctions, not prison. The criminal case against him focused on his failure as a cop, not as a doctor. If any of the jurors who convicted him ever have the misfortune of suffering pain severe enough to require strong medication, you can be sure they won't be looking for a good cop.