When Brahim al-Aouissaoui made a video call to his family back in Tunisia early on Thursday he told them he had just arrived in Nice and found a place to sleep in a stairwell near a church, they recalled.

Very soon afterwards, French police believe, the young Tunisian walked into the church and killed three people, beheading one of them, and shouting “Allahu Akbar” - God is the greatest in Arabic.