  We use two-body potentials derived from a constituent quark cluster model to
analyze the bound-state problem of the $\Sigma NN$ system. The observables of
the two-body subsystems, $NN$ and $\Sigma N$, are well reproduced. We do not
find $\Sigma NN$ bound states, but there are two attractive channels with a
resonance close above the three-body threshold. These channels are the
$(I,J)=(1,1/2)$ and $(0,1/2)$, their quantum numbers, widths and energy
ordering consistent with the recently measured strange tribaryons from the
$^{4}{\rm He}(K_{{\rm stopped}}^{-},N)$ reactions in the KEK PS E471
experiment.
