  The experimental data of the COSY-GEM Collaboration for the recoil-free
transfer reaction p (27Al, 3He) \pi - p' X, leading to the formation of bound
state of eta (\eta) meson in 25Mg nucleus, is reanalyzed in this paper. In
particular, predicted values of binding energy and half-width of the \eta
-mesic nucleus 25Mg\eta, given by different theoretical approaches, are
compared with the ones obtained from the experimental missing mass spectrum. It
is found that the spectrum can be explained reasonably well if interference
effect of another process, where \eta is not bound in 25Mg but is scattered by
the nucleus and emerge as a pion, is taken into account. The data also indicate
that the interaction between N*(1535) and a nucleus is attractive in nature.
