WASHINGTON, June 13, 2016 (Xinhua) -- Photo taken on June 12, 2016, shows a news conference held by FBI in Orlando, Florida, the United States. Volunteers queued for hours in heavy rain to donate blood at mobile stations in Orlando, Florida, where the deadliest U.S. mass shooting to date took place on Sunday, while politicians argued from the very wording of the incident to ways to prevent the recurrence of such tragedy. At least 50 people were killed and 53 others wounded, including a police officer in the attack early Sunday. (Xinhua)