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 \pm 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 .