  We report on follow-up observations of the GRB 060927 using the ROTSE-IIIa
telescope and a suite of larger aperture ground-based telescopes. An optical
afterglow was detected 20 s after the burst, the earliest rest-frame detection
of optical emission from any GRB. Spectroscopy performed with the VLT about 13
hours after the trigger shows a continuum break at lambda ~ 8070 A produced by
neutral hydrogen absorption at z~5.6. We also detect an absorption line at 8158
A which we interpret as SiII at z=5.467. Hence, GRB 060927 is the second most
distant GRB with a spectroscopically measured redshift. The shape of the red
wing of the spectral break can be fitted by a damped Lyalpha profile with a
column density with log(N_HI/cm^-2) ~ 22.5. We discuss the implications of this
work for the use of GRBs as probes of the end of the dark ages and draw three
main conclusions: i) GRB afterglows originating from z>6 should be relatively
easy to detect from the ground, but rapid NIR monitoring is necessary to ensure
that they are found; ii) The presence of large HI column densities in some GRBs
host galaxies at z>5 makes the use of GRBs to probe the reionization epoch via
spectroscopy of the red damping wing challenging; iii) GRBs appear crucial to
locate typical star-forming galaxies at z>5 and therefore the type of galaxies
responsible for the reionization of the universe.
