details. what are you learned? reporter: good morning, alyson. well, you can hear four hours since this incident occurred. overhead, police helicopters are still assessing the scene. this is an ongoing investigation. the lop don metropolitan police force said only there is a tracer that is being purr saoufd. no doubt given this is now fourth attack in the last sucks months that those in government are dealing with the reality of the propaganda value of these attacks and the ability to wreak this kind of havoc. this is is a residential area. it is miraculous that only 18 people were injured. we can show you the video of that improvised device. it is incredibly crude. it is the broader impact at this