Someone posted this on another thread, but oddly enough, the crime is not listed as unsolved on the DC Crime Solvers website...either the killer was apprehended, but no publication ever reported on it, or Quarles Harris simply didn't make the Unsolved/Major Crimes list of 2008:
http://mpdc.dc.gov/mpdc/cwp/view,a,1243,q,541992,mpdcNav_GID,1533.asp