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.
More top news
Nepal is reeling with shock, on edge and waiting for help to arrive after it was hit by the worst earthquake disaster in over 80 years.
Former Newsnight presenter Jeremy Paxman has said he no longer watches the programme but revealed he's a fan of dating show Take Me Out
Prince Harry will miss the birth of his new niece or nephew as he has flown back to Australia.