Transcript for Seven killed in vehicle attack on London Bridge

This is the third terror attack in the uk since March. What is going on? We want to bring in Brian Ross. Brian, this is the third attack since March, Terry just mentioned that. Can you put that in context with the others. It's a small comfort. Unlike the planning and training it took for the Manchester attack, this is a low-tech terror attack. It's the kind yisis has been telling followers to pull off. We saw this in March on the Westminster bridge in London. What you to make of the fact that one of the bombers was wearing a fake suicide vest. Sflit caused panic last night, for sure. It seemed to certainly guarantee that the attackers would be shot dead by police. The police training in these cases is, if you see someone with a suicide vest, three shots to the head. We also know that ISIS has been telling followers in their twisted version of Islam, to become a martyr in the month of ram Dan, which we're in, has benefits. Is there significance to the timing of the attack? But also, what is going on in the uk. They have foiled five more attacks since the Westminster bridge attack if March. As police carry out a series of raid this is morning, they suggest they have identified some of the three terror suspects. She said there's no known connection between last night's attack and any of the others. The but that terrorism breeds terrorism. The British have 500 aiskt terror cases under way right now. Terrifying way of saying it. Terrorism breeds terrorism. Chief investigative correspondent Brian Ross, thank you for coming in on a Sunday morning. We appreciate it.

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