Bilal Ahmed hides behind an envelope as he leaves court with his lawyers, Peggy Bennett and Barry Coburn, on Jan. 28, 2016. He is accused of sexually assaulting three patients while they were anesthetized. (Keith Alexander/The Washington Post)

A former Washington dentist who allegedly sexually assaulted three patients while they were anesthetized was indicted Tuesday, prosecutors said.

In 2014, Bilal Ahmed, 44, of Potomac was treating a male patient at Universal Smiles DC in the 2300 block of M Street NW when the patient, after being administered nitrous oxide through a face mask, realized Ahmed was sexually assaulting him, the U.S. Attorney’s Office for District of Columbia said in a statement.

The patient reported the assault to police, who found two other male patients who said Ahmed sexually assaulted them after treating them with nitrous oxide, the statement said. One of Ahmed’s employees also said the dentist improperly touched him, according to the statement.

Ahmed, who was arrested in January at John F. Kennedy International Airport in New York, was indicted on 21 counts of sexually abusing or otherwise improperly touching former patients and employees in 2013 and 2014, including 14 felony counts of sexual abuse, four misdemeanor counts of sexual abuse and three misdemeanor counts of assault, prosecutors said. His dental license was suspended in April.

Ahmed’s dental practice’s office manager, Mahsa Azimirad, 26, of North Bethesda, who allegedly lied to a grand jury during the Ahmed investigation, was also indicted on one count of perjury, according to prosecutors.

Ahmed and Azimirad pleaded not guilty at earlier court appearances.