  J.H. Koolen and J. Park have proved a lower bound for intersection number
$c_2$ of a distance-regular graph $\Gamma$. Moreover, they showed that the
graph $\Gamma$ which attains the equality in this bound is a Terwilliger graph.
We prove that $\Gamma$ is the icosahedron, the Doro graph or the Conway-Smith
graph, if equality is attained and $c_2\ge 2$.
