You may want to check the Digital Library on American Slavery to see if they have anything. I did a quick search of the name ARMSTRONG for All States and this was one of them:

PAR Number 20484002
State: District of Columbia Year: 1840
Location: Washington Location Type: County

Abstract: Joseph Armstrong, Peter Butler, Emanuel Price and Maria Coase assert that they are "coloured persons" of the state of Delaware who are "entitled to their freedom now, or will be in a short time" according to the laws of the state. They have been carried beyond the jurisdiction of Delaware and are now confined to the jail of a certain William H. Williams in the city of Washington. They believe that they are intended to be sold in "everlasting servitude." Therefore, they seek a writ of habeas corpus.

Don't know if this has anything to do with yours, but it may be worth a try to see if anything is there. I also came across some for the State of Maryland, but you may want to see those yourself.

Deloris