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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A team of detectives and specialists is set to begin a painstaking excavation of the area where Ben is thought to have gone missing in 1991.
The foreign secretary's suggestion last week's bombing of an aid convoy might constitute a war crime prompted an angry response from Moscow.
Goals from Charlie Austin, Dusan Tadic and James Ward-Prowse consigned Slaven Bilic's men to their fourth straight Premier League loss.