The retrial of William Hurwitz (the subject of my Findings column) began Monday looking like a rerun of the first trial as the prosecutor spouted familiar horror stories and waved the same red flags. But this is already looking like a tougher case for the prosecution.

Jonathan Fahey, one of the prosecutors in federal court in Alexandria, Va., told the jurors in his opening statement that Dr. Hurwitz was a drug trafficker — part of a drug-trafficking conspiracy, in fact — because he prescribed large quantities of OxyContin and other pills while ignoring clear “red flags” that his patients were misusing and reselling the pills. The prosecutor said that Dr. Hurwitiz’s prescribing was “without a legitimate medical purpose” and “in its wake it left destruction, devastation and death.”

Those were the arguments that persuaded jurors to convict Dr. Hurwitz of drug trafficking charges in 2004. The jury foreman, Ralph Craft, told the Washington Post after the trial that the prescribed dosages “went beyond the bounds of reason” and would never have been prescribed by a “legitimate doctor.” Dr. Hurwitz’s defense — that he genuinely believed his patients needed the medicine and didn’t realize he was being duped by drug addicts and dealers — didn’t work, in no small part because the judge told the jury it didn’t matter if he had acted in “good faith.”

The verdict vindicated the Drug Enfrocement Administration’s strategy of using the power of drug-trafficking laws against doctors prescribing opioids even when there was no evidence (as in Dr. Hurwitz’s case) that they were getting a cut of the illegal sales. Karen Tandy, the D.E.A. administrator, praised the 25-year sentence imposed on Dr. Hurwitz by saying he “was no different from a cocaine or heroin dealer peddling poison on the street corner.”

Since then, though, there have been a couple of different opinions about the intepretation of federal drug law. Last year the Supreme Court ruled that it applies to doctors only when they’re guilty of “drug dealing and trafficking as conventionally understood.” And an appeals court ordered a retrial for Dr. Hurwitz because the jury should have considered whether he acted in “good faith.”

So for this trial Dr. Hurwitz has a new argument — and a new defense team eager to use it as a mantra. He’s being represented by two experienced lawyers who are working pro bono: Richard Sauber, of Fried, Frank, Harris, Shriver & Jacobson, and Larry Robbins, of Robbins, Russell, Englert, Orseck & Untereiner.

Mr. Sauber used his opening statement to tell the jury over and over that the case boiled down to one question: Was Dr. Hurwitz a doctor or a drug dealer? Calling him a “passionate advocate for patients who had been unfairly treated,” Mr. Sauber talked about Dr. Hurwitz’s work in the Peace Corps and in Veterans Administration hospitals, and his belief that too many patients were in pain because doctors were afraid to give them proper dosages of opioids. Mr. Sauber also promised to do something that the defense didn’t effectively do in the first trial: use expert testimony to show that the dosages prescribed by Dr. Hurwitz were within the bounds of legitimate medicine.

The first day of the trial ended with the testimony of Cynthia Denise Horn, a former patient of Dr. Hurwitz, who was a prosecution witness. She said she had repeatedly faked pain in order to get him to prescribe OxyContin pills, which she used herself and also sold. When it was the defense’s turn to question her, Mr. Robbins resumed the doctor-or-drug-dealer mantra. As he went through her medical records, noting the regular examinations by Dr. Hurwitz and the questionnaires he had made her fill out about her pain, he repeatedly asked her to compare Dr. Hurwitz with the street dealers who had supplied her with OxyContin.

“Did any of the people who sold you drugs and medication ever ask you about your pain?” Mr. Robbins inquired. The prosecution objected, but the judge, Leonie Brinkema, directed Ms. Horn to answer.

“No,” she said. That wasn’t surprising, of course, but it was a good moment for the defense. It reminded the jury that there is at least some difference between a street-corner dealer and a doctor.