Zaghba was interrogated but was eventually released. An Italian official confirmed to the Guardian that Italian authorities alerted their British counterparts when Zaghba moved to London.

On his thwarted trip to Syria:

He was stopped at Marconi airport in Bologna on 15 March 2016 travelling with only a backpack and a one-way ticket to Istanbul, the newspapers said. He had told his mother he was going to Rome. He became agitated as he approached the check-in desk. According to La Repubblica, when he was challenged, he told officials: “I am going to be a terrorist”. His passport and mobile were impounded. Material found on his phone included propaganda videos and religious sermons that confirmed his wish to join Islamic State, the paper reported.

Authorities now believe this was a locally hatched plot that was not directed by ISIS or any other group.

Here's more on the second attacker, who had an Irish ID card.