Ricin threat: Cologne police search flats and only some aspects of the story are interesting

This BBC report https://www.bbc.co.uk/news/world-europe-44494010 starts thus:

'German police are searching flats in a Cologne tower block where a Tunisian man is suspected of having kept highly toxic ricin.

The 29-year-old man, named in German media only as Sief Allah H, is being questioned by police.'

The article goes on to query what ricin is and how it's linked to castor oil. What the report doesn't wonder is what possible motive might be behind this storage of ricin.