Denver officials said they are not aware of any threats made to President Barack Obama's campaign, but are exploring all possibilities as they investigate the shooting at his re-election headquarters.
Right now, no one is in custody and investigators are looking at surveillance video to see if a vehicle can be identified.
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As the world remembers the Holocaust, an Auschwitz survivor says he remains "fearful" following the attack on a Jewish supermarket in Paris.
Police are hunting four men who smashed their way into a jewellers in broad daylight and threatened staff with sledgehammers.
ComRes polling agency chairman says the next 100 days will be be gruelling in the most uncertain General Election that anyone can remember.