ROME - Italian police followed the correct procedures in flagging one of the London attackers to their British counterparts, Italy's senior policeman said on Wednesday, but he understands why the warning went unheeded.Three Islamist assailants, including Italian-Moroccan national Youssef Zaghba, killed eight people in central London on Saturday before they themselves were shot dead.Zaghba was identified as a possible militant threat after he was stopped at Bologna airport in 2016 as tried to reach Syria. He was not charged, but local police monitored him carefully and tipped off Britain when he subsequently moved to London."Our conscience is clear," Franco Gabrielli, the head of the national police, told reporters while visiting the southern island of Lampedusa.British authorities have said Zaghba had not been a subject of interest for them or the domestic intelligence agency MI5. Gabrielli said some police forces had been deluged with tip-offs about potential radicals, making it possible for some to slip beneath the radar."It is very easy to speak with hindsight," he said. "The issue of flagging (threats) is extremely complex and strictly tied to the amount of information that any one country is called on to process, which in some cases is an enormous amount. "That is why I am not going to criticize the behavior of others."Zaghba's Italian mother, Valeria Khadija Collina, told reporters that she had informed police her son was missing after Saturday's attack. She said she thought he might have gone into hiding because she was aware he knew one of the slain attackers."I was afraid. I thought, what is going to happen? Is he going to hide for the rest of his life?" she said, adding that she was horrified when she realized he had taken part in the assault and felt the anguish of the victim's families."I understand deep down, inside my heart, the pain of these people," she said, speaking at her home near the northern city of Bologna. She promised to work in future to dissuade other young Muslims from going down the road of radicalisation."I will try, from this moment on, to do all I can to make sure these things are not repeated."