A graph is said to have optimal vertex connectivity if its vertex connectivity equals its minimum degree. According to this arXiv preprint, it was shown by Mader in (Arch. Math., 1970) and (Math. Ann., 1971) that a connected vertex-transitive graph without $K_4$ has optimal vertex connectivity. My question is: which of the two papers by Mader mentioned above proves this result, and what is the exact statement of this result?

This result implies that all connected vertex-transitive graphs with clique number 2 or 3 have optimal vertex connectivity. In particular, all connected Cayley graphs generated by transpositions (these graphs are bipartite) have optimal vertex connectivity.