Some of the people alleged to have been killed by lethal injection were in the Lakeside acute care patients’ unit at Memorial, Mr. Foti said.

Test results on the bodies of the victims found morphine and midazolam hydrochloride, according to the affidavit. Midazolam, commonly known by its brand name Versed, is sometimes used in patients in intensive care units to cause unconsciousness before and during surgery.

An exchange of dialogue quoted in the affidavit between Dr. Pou and an unidentified nurse executive said Dr. Pou told her: “decisions had been made to administer lethal doses” to patients remaining on the seventh floor of the unit who would not survive.

One patient reportedly said “that burns” when injected. A statement from the Tenet Healthcare Corporation called the accusations that the three might have administered pain medication to hasten the deaths of certain patients “disturbing.”

“If the allegations are proven true, the doctor and nurses named by the attorney general made these decisions without the knowledge, approval or acquiescence of the hospital or their key physician leaders,” the Tenet statement said.

A lawyer for Dr. Pou, Rick Simmons, said that the authorities went to her house in Baton Rouge and arrested her in her scrubs. She went through the booking process and was later released, he said.

Mr. Simmons said that the arrest warrants were issued on four counts for each of the women but that there were no formal charges yet.