A timer was attached to the homemade bomb used in the Parsons Green terror attack, according to reports.
The improvised explosive device may have been detonated on the rush-hour Tube train remotely, security sources told the BBC and Sky News.
The bomb, which injured at least 22 people, is thought to have failed to properly ignite.
Police are combing through CCTV footage from the London Underground network after launching a manhunt for the person planted the device, which was carried inside a Lidl freezer bag.
Pictures posted on social media appeared to show wires emerging from a bucket filled with chemicals on the floor of the carriage.
Explosive experts told the BBC the images appeared to show “deflagration” – in which a substance burns away rapidly – rather than detonation, which would have killed anyone nearby.
It is believed police could be helped “considerably” by the fact the device was not destroyed by the blast.
Detectives are investigating whether the attacker left the District line train before it reached Parsons Green or fled amid the chaos as the blast sparked a stampede among panicked commuters.
Passengers were “pushed and trampled on” as they sought to escape from the train, according to witnesses.
Most of the 22 people taken to hospital suffered “flash burns” in the explosion, said Metropolitan Police Assistant Commissioner Mark Rowley. Via: Independent UK
Meanwhile, the left seems to be more concerned about President Trump’s response to the terror attack than the attack itself.
President Trump tweeted:
Leftist media outlets like CNN responded in the manner in which most of America has come to expect.
— CNN International (@cnni) September 15, 2017
London resident Paul Joseph Watson responded to the left’s attack on Trump:
If you're more outraged about Trump's tweet than the terror attack, you're part of the problem. #London
— Paul Joseph Watson (@PrisonPlanet) September 15, 2017