  We report the detection of CO emission from the optically luminous,
radio-quiet quasar J140955.5+562827, at a redshift z_CO =2.583. We also present
VLA continuum mapping results and VLBA high spatial resolution observations at
1.4 GHz. Both the CO(3-2) and CO(7-6) emission lines are detected using the
IRAM Plateau de Bure interferometer. The 3-2/7-6 line luminosity ratio is about
1/3 indicating the presence of warm and dense molecular gas with an estimated
mass of 6x10^10 Msun. The infrared-to-CO luminosity ratio is L_FIR/L'_CO(1-0)
\approx 500 Lsun (Kkms^-1 pc^2)^-1,comparable with values found for other
high-z sources where CO line emission is seen.
  J1409+5628 is detected using the VLA with a 1.4 GHz rest-frame luminosity
density of 4.0x10^25 W Hz^-1. The radio to far-infrared ratio, q, has a value
of 2.0 which is consistent with the values found in star forming galaxies. At
the 30 mas resolution of the VLBA, J1409+5628 is not detected with a 4 sigma
upper limit to the surface brightness of 0.29 mJy beam^-1. This implies a limit
to the intrinsic brightness temperature of 2x10^5 K at 8 GHz, typical for
nuclear starbursts and two or more orders of magnitude weaker than typical
radio-loud active galactic nuclei. Both the properties of the CO line emission
and the radio emission from J1409+5628 are therefore consistent with those
expected for a star forming galaxy.
  In J1409+5628 young massive stars are the dominant source of dust heating,
accounting for most of the infrared luminosity, and the massive reservoir of
molecular gas can sustain the star formation rate of a few 1000 \Msun yr^-1
implied by the far-infrared luminosity for about 10 million years.
