We report calculated photodetachment cross sections from the metastable ${\mathrm{Be}}^{\ensuremath{-}}$ ${1s}^{2}{2s2p}^{2}$ ${}^{4}{P}^{e}$ state in the photon energy range 0--10 eV. Outer-shell photodetachment takes place in this energy range, which includes the double-ionization threshold ${\mathrm{Be}}^{+}{(}^{2}{S}^{e})$ at $\ensuremath{\sim}7\mathrm{eV}$ as well as doubly excited thresholds of the residual atom up to the $\mathrm{Be}{(1s}^{2}2p4f)$ threshold at $\ensuremath{\sim}10\mathrm{eV}.$ Therefore, triply excited states of ${\mathrm{Be}}^{\ensuremath{-}}$ are reached within the selected photon energy. We have implemented the complex scaled configuration interaction method along with a model potential for the ${1s}^{2}$ core to uncover the first series of ${\mathrm{Be}}^{\ensuremath{-}}$ ${}^{4}{L}^{o}$ resonant states. In this work, four ${}^{4}{P}^{o},$ seven ${}^{4}{D}^{o},$ and two ${}^{4}{S}^{o}$ resonances are reported and we compare our cross section with other previous theoretical calculations, that reported none or, at most, two resonances.