April 19, 1865 funeral procession

[STS Lincolnite]

I decided to come at this a litte sideways and looked for other pictures of the Union Army Grand review and found some here:

http://www.loc.gov/pictures/item/2004667344/

I think the summary of the photo group (posted below) gives some clues as to the nature of the photo you found Kees.

Summary: The Grand Review of the Union army held in Washington , D.C. Crowds of spectators, some with umbrellas; large groups of mounted soldiers; troops and presidential reviewing stands on Pennsylvania Avenue; the Capitol festooned with crepe and with its flag at half-mast. Includes nine stereographs by E. & H. T. Anthony from Brady negatives.

There is no specific date given (just 1865), but it seems that the Capitol was in fact decorated with crepe and the flag was at half-mast. In thinking on this a little further, the use of crepe and the flag put at half-mast during the grand review may have been considered and used as a show of respect for the Union Armies' comrades who lost their lives during the war. What do you think?