A complicated story that illustrates the dangers of HUMINT and the source's death suggests he was in very deep - as this passage shows:
Es Satty became a CNI informant in 2014, three years before the attacks in exchange for his not being deported after he served four years in prison for drug trafficking. He died in a blast in the town of Alcanar the day before the attacks when a stockpile of the terrorists’ explosives accidentally went off.
Link:https://www.thenational.scot/news/17...nt-s-position/

Plus the rivalry between national and local / regional police forces (which appears quite often).