We are exploring the viability of the collapsar model for long-soft gamma-ray bursts. We perform general relativistic hydrodynamic simulations in a dynamically evolving space-time with the CoCoNuT code. We start from massive low metallicity stellar models evolved up to core gravitational instability, and then follow the subsequent evolution until the system collapses forming a compact remnant. We have implemented a leakage scheme for this metastable high-mass neutron star to cool down and collapse by fall-back to a black hole. We show that sufficiently fast rotating cores lead to the formation of Kerr BHs, due to the fall-back of surrounding matter still bounded in this failed CCSN scenario.