A man was found guilty of second-degree murder Thursday in the killing of his mother and step brother in Prince George's County.

Quindell Mercer, 35, went to the Fort Washington home of Patricia Harris and her son, Frank Lamar Harris, on Aug. 3, 2011 and shot them both, leaving their bodies on a couch so that it appeared they were sleeping, according to prosecutors.

Frank Arthur Harris discovered his wife and son dead in the home the next day.

Although prosecutors lacked a clear motive in the case, they were able to identify a handgun used to kill Mercer's mother and half-brother -- a Desert Eagle .45-caliber handgun -- as one of four guns Mercer threw out of a window when he was arrested in August 2011, according to authorities.

Mercer was convicted of two-counts of second degree murder and several other handgun related charges in Prince George's County Circuit Court.

Mercer is scheduled to be sentenced Jan. 11 and faces 110 years in prison.