The mechanism for formation of the Earth's radiation belts has been an outstanding issue for utilization of the geospace environment. We present a magnetic storm recovery phase that occurred from 10 to 19 October 1990, in which there is a clear correlation among continuous injection of hot electrons, generation of chorus, geomagnetic AE activity (all for ∼8 days) and the acceleration of electrons to relativistic energies. We propose a following scenario to explain the observations: the continuous injection of hot electrons associated with the continuous AE activity. The hot electrons with Tperp/Tpara > 1 temperature anisotropies excite whistler-mode chorus waves. The chorus interacts with energetic electrons accelerating them to MeV energies forming a flux of “killer electrons” in the outer radiation belt.