Second arrest made in London Underground terror attack

The UK's terror-threat level remains at critical while details still emerge about one the key suspects.
2:22 | 09/17/17

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Transcript for Second arrest made in London Underground terror attack
A major new development in the London subway bombing. Police say they have take an 21-year-old man into custody. This comes after raids in a suburb of London, as sna search for crews to find who set off a crude bomb frud. Reporter: Good morning, Dan. Good morning, Paula. This is where London's counterterrorism command is working round the clock to find out who is responsible for Friday's bombing. New details starting to emerge about one of the key suspects. Overnight, a second arrest made in the London train bombing. An attack that left 30 people injured. A 21-year-old man was taken by anti-terrorism police in west London just before midnight. Police earlier raided a home near London yesterday. Police! Come to the front door now! Reporter: Officers swooping into this normally peaceful neighborhood after an 18-year-old suspect was arrested. Neighbors in the area evacuated for their own safety. I was scared for -- to be honest. Reporter: That's 12 miles away from parsons green. The site of the E ploexplosion. We urge the public to E main vigilant. He was arrested on suspicion of being concerned of acts of terrorism. He's now been transferred to custody at a police station in London. Reporter: The homemade device con caned nails and TATP. Made from hydrogen per Rox id, commonly used as hair bleach. This has been used in terror takes before. Including the Manchester bombing at the Ariana grande concert that killed 22. Well, what we're hearing now is the 18-year-old suspect may well have already been known to the police. Though, that's not confirmed at this stage. That's what the media here are reporting. The terror threat level reminds hi remains high. We want to bring in chief anchor, George Stephanopoulos. Who hosts "This week" later this

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

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