Obama on Batman cinema shooting in Denver, Colorado
20 July 2012 Last updated at 16:39 BST
President Barack Obama has said it is a "day for reflection and prayer" before leading a moment's silence in the wake of the mass shooting at a Denver cinema on Thursday night.
Speaking at what was going to be a campaign event, he said, "we may never understand what leads anybody to terrorise their fellow human beings like this... life is very fragile. Our time here is limited and it is precious."