>> Developments in the manhunt for suspects in the London Underground bombing, as British Police arrest an 18-year-old man. They made what they describe as a significant arrest on Saturday, in the town of Dover's port area, where ferries depart for France. Friday's attack pushed the UK threat level up to critical, meaning another attack may be imminent.
29 people were hurt when a homemade bomb burst into flames on a packed commuter train, prompting a stampede to get out of Parsons Green Station. The improvised bomb on the London train apparently failed to fully detonate. The West London tube station reopening Saturday. Islamic State has claimed responsibility for the attack.
UK police treating the bombing as terrorism, the country's fifth such attack this year. This one was a lucky escape.>> For this period, military personnel->> UK Prime Minister Theresa May announcing troops would guard strategic sites, freeing up hundreds of police to work round the clock on the investigation.
Trawling through surveillance footage, speaking to witnesses and examining what's left of the device. Pictures and video from the scene showing a plastic bucket with wires sticking out of it. Chip Chapman is the former head of counter-terrorism at the Ministry of Defense.>> Well, what you can say is this was partially functioned IED, or improvised explosive device.
Something went wrong, either in terms of the composition of the device. Normally, if it was IS, they use a preferred explosive called TATP, triacetone triperoxide. So either the mix, the chemical composition of that went wrong, or the detonator wasn't powerful enough to give a boost for this.>> Officials won't say whether the bomber was on the train when the blast went off.
Islamic State claimed three other attacks in the UK this year. Two in London, and one at an Ariana Grande concert in Manchester in May that killed 22 people, most of them teenage fans.