Comment on “Bound-state eigenenergy outside and inside the continuum for unstable multilevel systems”

We discuss the solution of the basic equations of the $N$-level Friedrichs model by using the Feshbach projection operator (FPO) technique and consider the relation between bound states in the continuum (BICs) and form factors. In the FPO formalism, the BICs are eigenstates of a non-Hermitian Hamilton operator with vanishing decay width. The wave function of a BIC is localized inside the system. On the basis of the FPO solutions we discuss the mechanism to yield a BIC at every coupling strength between system and environment. We relate our results to those given by Miyamoto [Phys. Rev. A 72, 063405 (2005)].