The installation of CCTV cameras on the the Tube could play a key role in finding the perpetrator of the Parsons Green explosion.
S7 trains such as the one involved in Friday's incident have video cameras installed inside all seven carriages.
There are a total of more than 12,000 cameras across London Underground's stations and trains.
The footage is managed and recorded locally, although British Transport Police say they can also view much of it at their hub to "develop intelligence about particular locations and suspects".
CCTV can allow them to "identify and follow suspects" and provide "powerful evidence in court", according to the force.
Detectives could scour footage from the tens of thousands of cameras across London as a whole in a bid to trace whoever is behind the blast.