  We explicitly construct cusp forms on the orthogonal group of signature
$(1,8n+1)$ for an arbitrary natural number $n$ as liftings from Maass cusp
forms of level one. In our previous works, the fundamental tool to show the
automorphy of the lifting was the converse theorem by Maass. In this paper, we
use the Fourier expansion of the theta lifts by Borcherds instead.
  We also study cuspidal representations generated by such cusp forms and show
that they are irreducible and that all of their non-archimedean local
components are non-tempered while the archimedean component is tempered, if the
Maass cusp forms are Hecke eigenforms. The standard $L$-functions of the cusp
forms are proved to be products of symmetric square $L$-functions of the
Hecke-eigen Maass cusp forms with shifted Riemann zeta functions.
