  We present one additional study of multi-muon events produced at the Fermilab
Tevatron collider and recorded by the CDF II detector. We use a data set
acquired with a dedicated dimuon trigger and corresponding to an integrated
luminosity of 3.9 fb$^{-1}$. We investigate the distribution of the azimuthal
angle between the two trigger muons in events containing at least four
additional muon candidates to test the compatibility of these events with
originating from known QCD processes. We find that this distribution is
markedly different from what is expected from such QCD processes and this
observation strongly disfavours the possibility that multi-muon events result
from an underestimate of the rate of misidentified muons in ordinary QCD
events.
