New Orleans ? Three days after Hurricane Katrina, floodwaters turned Memorial Medical Center from a hospital surrounded by live oaks and historic homes to a grim island where a doctor and two nurses are accused of making a momentous decision: Not everyone could be saved.

Staff members and hundreds of patients were stranded inside the sweltering building awaiting rescue. The power was out, the toilets were backing up, and 10 feet of putrid floodwaters filled the neighborhood. Some patients watched from their beds as people broke into nearby buildings in the lawless streets outside.

On Tuesday, a doctor and two nurses who labored in the storm’s chaotic aftermath were accused of murdering four trapped and desperately ill patients with injections of morphine and sedatives.

“We’re talking about people that pretended that maybe they were God,” Louisiana Atty. Gen. Charles Foti said. “And they made that decision.”

The defendants were booked on charges of being “principals to second-degree murder,” which carries a mandatory sentence of life in prison.

The three were the first medical professionals charged in a monthslong criminal investigation into whether many of New Orleans’ sick and elderly were abandoned or put out of their misery in the days after the storm.

An airboat pulls up to help evacuate patients and staff at Memorial Medical Center in New Orleans in this Aug. 31 file photo. A doctor and two nurses have been arrested in connection with the deaths of patients at the hospital in the days following Hurricane Katrina.

Dr. Anna Pou, a cancer and ear, nose and throat specialist, and the two nurses were accused of deliberately killing four patients, ages 62 to 90, with a “lethal cocktail” of morphine and the sedative Versed. The patients’ names were not released.

“There may be more arrests and victims that cannot be mentioned at this time,” Foti said. “This case is not over yet.” He planned to turn the case over to the New Orleans district attorney, who will decide whether to ask a grand jury to bring charges.

Memorial Medical had been cut off by flooding after the Aug. 29 hurricane swamped New Orleans. Power was knocked out in the 317-bed hospital and the temperature inside rose to more than 100 degrees as the staff tried to tend to patients who waited four days to be evacuated.

In court papers, state investigators said Pou told a nurse executive three days after the hurricane that the patients still awaiting evacuation would probably not survive and that a “decision had been made to administer lethal doses” to them. Overdoses of morphine or Versed can stop the heart and lungs.

Attorneys for the three insisted no crime took place; one praised his client’s dedication during the crisis.

Two months after the hurricane, Foti subpoenaed more than 70 people in an investigation into rumors that patients had been put to death at the medical center, where search teams recovered 40 bodies.

Around the same time, the husband-and-wife owners of a nursing home in neighboring St. Bernard Parish were charged with negligent homicide in the deaths of 34 elderly patients. Prosecutors said the owners failed to heed warnings to evacuate.

According to court papers, tissue samples taken from the dead at Memorial Medical tested positive for morphine and Versed, and the amount of Versed present was found to be higher than the usual therapeutic dose. Medical records reviewed by investigators also showed that none of the four patients were taking either of the two drugs as part of their routine care.

Foti said authorities could not determine which of the defendants actually administered the fatal drugs in each case but that investigators believe all three participated, hence the “principal to second-degree murder” booking.