A former doctor at the District of Columbia jail has pleaded guilty to sexually assaulting a male inmate.

Dr. Lewis Jackson, 36, faces a maximum of 20 years in prison. Tuesday's guilty plea came three months after Jackson pleaded guilty in federal court in Atlanta to sexually assaulting three inmates at the United States Penitentiary in Georgia.

According to prosecutors in D.C., on Nov. 10, 2008, Jackson sexually assaulted an inmate when he went to him for medical care. The victim immediately reported the matter to authorities at the D.C. jail.

The government secured Jackson's indictment last year after developing DNA evidence.

Within weeks of Jackson's indictment in the District, he was indicted for similar crimes in federal court in Atlanta. Jackson, who worked at the federal penitentiary from January 2011 through July 2012, admitted that he sexually abused the three inmates in October 2011. He is to be sentenced in Atlanta on Feb. 7, 2013.

His sentencing in the District will be scheduled after those proceedings.