The Italian daily Corriere della Sera, which was first to identify Mr. Zaghba on Tuesday, reported that he had been stopped by the authorities in the Bologna airport in March 2016 while he was trying to travel to Turkey and on to Syria to fight for the Islamic State.
The newspaper said that the Italian government had notified the British government about its concerns, and that Mr. Zaghba had been working at a restaurant in London.
If confirmed, that report is likely to add to pressure on the British government over its monitoring of Mr. Butt, a British citizen born in Pakistan. The London police, however, said that Mr. Zaghba “was not a police or MI5 subject of interest,” referring to Britain’s domestic intelligence agency.