  In 2 + 1 flavour lattice QCD the spectrum of the nucleon is presented for
both parities using local meson-baryon type interpolating fields in addition to
the standard three-quark nucleon interpolators. The role of local five-quark
operators in extracting the nucleon excited state spectrum via correlation
matrix techniques is explored on dynamical gauge fields with $m_\pi$ = 293 MeV,
leading to the observation of a state consistent with the S-wave $N\pi$
scattering threshold in the negative-parity sector. Furthermore, the robustness
of the variational technique is examined by studying the spectrum on a variety
of operator bases. Fitting a single-state ansatz to the eigenstate-projected
correlators provides robust energies for the low-lying spectrum that are
essentially invariant despite being extracted from qualitatively different
bases.
