  The missing-mass spectrum obtained in a recoil-free transfer reaction
p($^{27}$Al,$^{3}$He)$\pi^{-}$p'X is analyzed. We find that the observed peak
structure arises from the coherent contributions from two reaction processes in
the energy region corresponding to a bound eta ($\eta$) meson. In one of the
processes the intermediate $\eta$ is captured by the nucleus to form the
$\eta$-mesic nucleus $^{25}$Mg$_{\eta}$. In the other process, the $\eta$ does
not form $\eta$-nucleus bound state. The interference between these two
processes has caused the peak of the spectrum to appear at an $\eta$ binding
energy stronger than the actual one. Our analysis also indicates that the data
are consistent with an attractive N*(1535)-nucleus interaction at energies
below the $\eta$N threshold.
