Upon examination of cell phone videos, it appears a bobby missed the knife yielding muslim nazi with a taser due to lack of range.
Only when the demented cockroach charged them where they able to partially subdue him with another taser shot.
As many people criticize citizens and security forces in the US and Israel for shooting instead of using tasers again knife wielding maniacs, this London Tube incident demonstrates the ineffectiveness of such non-lethal weapons beyond close range.
If the muslim terrorist was rigged with an explosive vest, they wouldn't have been able to neutralize him in time.