  Context. A solar eruption on 17 April 2021 produced a widespread Solar
Energetic Particle (SEP) event that was observed by five longitudinally
well-separated observers in the inner heliosphere at heliocentric distances of
0.42 to 1 au: BepiColombo, Parker Solar Probe, Solar Orbiter, STEREO A, and
near-Earth spacecraft. The event produced relativistic electrons and protons.
It was associated with a long-lasting solar hard X-ray flare and a medium fast
Coronal Mass Ejection (CME) with a speed of 880 km/s driving a shock, an EUV
wave as well as long-lasting radio burst activity showing four distinct type
III burst. Methods. A multi-spacecraft analysis of remote-sensing and in-situ
observations is applied to attribute the SEP observations at the different
locations to the various potential source regions at the Sun. An ENLIL
simulation is used to characterize the interplanetary state and its role for
the energetic particle transport. The magnetic connection between each
spacecraft and the Sun is determined. Based on a reconstruction of the coronal
shock front we determine the times when the shock establishes magnetic
connections with the different observers. Radio observations are used to
characterize the directivity of the four main injection episodes, which are
then employed in a 2D SEP transport simulation. Results. Timing analysis of the
inferred SEP solar injection suggests different source processes being
important for the electron and the proton event. Comparison among the
characteristics and timing of the potential particle sources, such as the
CME-driven shock or the flare, suggests a stronger shock contribution for the
proton event and a more likely flare-related source of the electron event.
Conclusions. We find that in this event an important ingredient for the wide
SEP spread was the wide longitudinal range of about 110 degrees covered by
distinct SEP injections.
