Barbara Jean Dreher disappeared in August 1984. She worked in Washington DC, was last seen in DC and her car was later found in Southwest DC.
The case summary mentions that she sometimes visited or stayed with her estranged husband who lived in Hillcrest Heights. Hillcrest Heights is actually in Prince Georges County, Maryland just south of the DC line.
Detective James Trainum is the investigator for this case. He is also mentioned in other DC cold cases here on Websleuths, including The Freeway Phantom killings and the disappearance of Shaquilla Bell.