All 3 London Bridge attackers have been identified

People who knew ringleader Khuram Butt say he was inspired in part by online preachings of a radical American Muslim cleric.
2:06 | 06/06/17

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Transcript for All 3 London Bridge attackers have been identified
followers to target law enforcement. This comes after the terror attack in London. The knife attacks that followed. Why so many attacks in so little time and tonight the major warning signs missed as authorities now brace for more and could any of these attackers come to the U.S. With the same plan. Here's ABC's chief investigative correspondent Brian Ross. Reporter: With these new scenes in Paris, and just days after the London bridge rampage, authorities tonight are asking if a new wave of terrorism is about to hit Europe. The fact is, however good the police are at responding, the attacker always gets the first blow. Reporter: Authorities tonight have now named all three London attackers, identifying the 22-year-old Moroccan man, Youssef zaghba. Like the ringleader khuram butt, he too was well known to British authorities as a potential threat. Especially after he had tried to go to Syria to join ISIS. But neither he nor butt were being tracked by the British, nor were they on any U.S. Watch list either. Which the homeland security secretary today said, means the U.S. Was also vulnerable. They would have certainly been able to buy a ticket and fly to the United States. Reporter: Also tonight, new pictures and accounts of khuram butt, and his confrontational behavior reported to police again and again. The person whose family took these pictures said, he called police last year after a physical confrontation with khuram butt, who called him a bad Muslim for supporting gay marriage. He ran at me with an expression of hatred in his face. A scuffle broke out, and at one point I helped wrestle him to the ground. He was full of hate. Brian is back with us tonight. We heard so many people who have complained to police about that man before the attack. Police have acknowledged they're overwhelmed. That's rights are David. There are some 3,000 people in Britain considered the highest priority threat and another 20,000 they're trying to keep an eye on. 23,000 in all. Every day they have to make a decision about who's the greatest threat. 23,000 cases. Brian, thank you.

This transcript has been automatically generated and may not be 100% accurate.

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