  We investigate the role of the environment in processing molecular gas in
radio galaxies (RGs). We observed five RGs at $z=0.4-2.6$ in dense Mpc-scale
environment with the IRAM-30m telescope. We set four upper-limits and report a
tentative CO(7$\rightarrow$6) detection for COSMOS-FRI 70 at $z=2.63$, which is
the most distant brightest cluster galaxy (BCG) candidate detected in CO. We
speculate that the cluster environment might have played a role in preventing
the refueling via environmental mechanisms such as galaxy harassment,
strangulation, ram-pressure, or tidal stripping. The RGs of this work are
excellent targets for ALMA as well as next generation telescopes such as the
James Webb Space Telescope.
