  The Keck optical spectrum of the GRB 020813 afterglow is the best ever
obtained for GRBs. Its large spectral range and very high S/N ratio allowed for
the first time the detection of a vast variety of absorption lines, associated
with the circumburst medium or interstellar medium of the host. The remarkable
similarity of the relative abundances of 8 elements with the dust depletion
pattern seen in the Galactic ISM suggests the presence of dust. The derived
visual dust extinction A_V=0.40+/-0.06 contradicts the featureless UV spectrum
of the afterglow, very well described by a unreddened power law. The
forthcoming Swift era will open exciting opportunities to explain similar
phenomena in other GRB afterglows.
