Abstract: The highest energies of solar energetic nucleons detected in space or through gamma-ray emission in the solar atmosphere are in the GeV range. Where and how these particles are accelerated is still controversial. The candidate processes are related to magnetic reconnection in a flare or a coronal mass ejection (CME), and to the shock wave driven by a fast CME. We search for observational indications on the acceleration site, using the relative timing of radio emissions in the corona and of relativistic protons at the Earth. We model the particle transport under the effects of focussing by an average Archimedean magnetic field and of scattering by its fluctuations, and use radio time profiles as injection functions. The predicted time profiles of the intensity and anisotropy of relativistic protons at 1 AU during the 20 Jan 2005 event are compared with neutron monitor observations. We compare the results with other events and discuss the nature of the prompt and delayed proton releases that have been identified in neutron monitor recordings of relativistic solar particle events.