On a 5-design related to an extremal doubly even self-dual code of length 72

It is shown that if there is a self-orthogonal 5-(72,16,78) design, then the rows of its block-point incidence matrix generate an extremal doubly even self-dual code of length 72. In other words, a putative extremal doubly even self-dual code of length 72 is generated by the codewords of minimum weight.