US Capitol Police say they have re-opened the Hart Senate building, following an evacuation.
Tests on a suspicious package were negative, Reuters reports.
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ITV News Economics Editor Noreena Hertz said an economic slowdown looms after price rises and lower spending led to gloomy figures.
Detectives in Westminster are investigating after the man was discovered on the Route 189 bus in Marylebone shortly after midnight.
The murderer was shaking and appeared to be gasping for air for around 13 minutes before dying.