NEW YORK (AP) — A prominent former New York City emergency room doctor already charged with sexually assaulting two women in his care has been indicted on additional charges of sex abuse for assaulting two more women he treated, prosecutors announced Thursday.

David Newman, who wrote a book on the patient-doctor relationship and claims to have served in a combat hospital in Iraq, victimized the women at Mount Sinai Hospital on three separate occasions last August, September and October as well as a fourth woman in January, according to court papers. In one case Newman injected a woman with pain killers and then masturbated on her, the papers charge.

"I would like to thank these brave women for their strength in coming forward," said Manhattan District Attorney Cyrus R. Vance Jr., who called the woman's abuse while under sedation by a doctor a patient's "nightmare scenario."

Newman, 45, of Montclair, New Jersey, now faces a total of five counts of sex abuse, four in the third degree and one in the first degree. He has pleaded not guilty to all of the counts. His attorney didn't immediately return a message seeking comment on the charges. A hospital spokeswoman says Newman no longer works at Mount Sinai and records show his medical license was suspended in February amid a state medical board investigation.

The investigation into Newman began after a woman who was treated for shoulder pain in January told police Newman gave her morphine and then masturbated on her. In a civil lawsuit filed in state Supreme Court last month, the woman claims a swab of semen collected from her face has tested positive for Newman's DNA. The woman, through her attorney, declined to comment. The Associated Press does not name victims of alleged sexual assault without their consent.

Newman told a detective in January when asked about the allegations that he was "embarrassed" because he had masturbated in the emergency room lounge and said "it was possible that the ejaculate may have gone from my hands to the woman's blanket," according to a court filing by prosecutors.

"I can't believe this is happening," he told the detective, according to the court filing. "What you are saying I did doesn't make sense either."

Following his arrest, the other women, whose ages ranged from 18 to 29 and were treated in the emergency room for headache, a cold, and a rash, came forward alleging they were similarly abused by Newman at Mount Sinai, authorities said.

Newman is the author of "Hippocrates' Shadow: Secrets From the House of Medicine," a book that examines "the fraying of patient-doctor relations" and advocates a "new paradigm to rebuild the bridge between physicians and their patients."

Newman described himself as "an emergency room physician, an Army veteran who was deployed to a combat support hospital in Baghdad in 2005, and a biomedical researcher in the field of cardiac-arrest resuscitation" in a 2013 New York Times op-ed piece advocating stricter gun control.