NEW ORLEANS (AP) – A grand jury refused on Tuesday to indict a doctor accused of murdering four seriously ill hospital patients with drug injections during the desperate aftermath of Hurricane Katrina, closing the books on the only mercy-killing case to emerge from the storm.

Dr. Anna Pou acknowledged administering medication to the patients but insisted she did so only to relieve pain.

Dr. Pou (pronounced “Poh”) and two nurses were arrested last summer after Attorney General Foti concluded they gave “lethal cocktails” to four patients at the flooded-out, sweltering Memorial Medical Center after the August 2005 storm.

The decision was a defeat for Mr. Foti, who accused the doctor and the nurses, but it was the New Orleans district attorney who presented the case to the grand jury, asking it to bring murder and conspiracy charges.

“I feel the grand jury did the right thing,” said District Attorney Eddie Jordan.

Charges against the nurses, Lori Budo and Cheri Landry, were dropped after they were compelled to testify last month before the grand jury under legal guidelines that kept their testimony from being used against them.

Many people in New Orleans believed the three acted heroically under punishing conditions. Last week, a group of doctors and nurses held a rally on the anniversary of Dr. Pou’s arrest, and hundreds of people turned out to show support.

“You look at a lady who’s trying to help the community, and they try to indict her,” said Clarence Singleton, who was selling seafood lunches Tuesday near the Louisiana Superdome.

Dr. Pou and the district attorney who oversaw the case were to speak at news conferences later Tuesday.

In an interview last fall with CBS’ “60 Minutes,” Dr. Pou said: “I’ve spent my entire life taking care of patients. I have no history of doing anything other than good for my patients.”

In a December 2005 interview, she told WBRZ-TV of Baton Rouge: “There were some patients there who were critically ill who, regardless of the storm, had the orders of do not resuscitate. In other words, if they died, to allow them to die naturally, and to not use heroic methods to resuscitate them.”

“We all did everything in our power to give the best treatment that we could to the patients in the hospital to make them comfortable,” Dr. Pou told the station.

Ms. Budo’s attorney, Eddie Castaing, called the grand jury’s decision proof that none of the three should ever have been arrested.

When the levees broke in New Orleans, 80 percent of the city flooded. The lower level of Memorial Medical Center was under 10 feet of water, and electricity was out across the city. Inside the hospital, the temperature topped 100 degrees.

At least 34 people died at the hospital, many from dehydration during the four-day wait for rescuers. In the “60 Minutes” interview, Dr. Pou stressed: “Anytime you provide pain medicine to anybody, there is a risk. But as I said, my role is to help them through the pain.”

Other doctors who were there described the situation as resembling a MASH unit during wartime rather than an urban American hospital.

“It was stifling. We were hoisting patients floor to floor on the backs of strong young men. It was as bad as you can imagine,” Dr. Gregory Vorhoff, who stayed throughout the storm and eventually hitched a ride on a boat to seek help, told The Associated Press after Pou was arrested.

The four patients Dr. Pou was accused of killing ranged in age from 61 to 90. Foti said all four would have survived if they had not been given morphine and midazolam hydrochloride.

Autopsies were performed, but the results were not released because of the grand jury investigation.

Dr. Pou, whose specialty is eye, ear, nose and throat surgery, gave up her private practice after she was arrested and has been teaching at LSU medical school in Baton Rouge.

The families of people who died at Memorial in the days after Katrina can still sue Dr. Pou.

Assistant Attorney General Cullen, who sat in on the grand jury hearings, said investigators in her office still consider the deaths to be homicides.