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Chris Murphy.
Murphy said his "heart goes out to the victims, their families, the first responders, and the entire Las Vegas community."
"Nowhere but America do horrific large-scale mass shootings happen with this degree of regularity. Last night's massacre may go down as the deadliest in our nation's history, but already this year there have been more mass shootings than days in the year," he said.
Mass attacks have happened in other countries, such as the November 2015 terrorist attacks in Paris, where 130 civilians were killed.
However, Monday's attack at the Jason Aldean country music concert in Las Vegas quickly became designated as the most deadly shooting by a sole perpetrator in US history, prompting Murphy to call for increased gun control measures. He did not specify what those measures would entail.
"This must stop. It is positively infuriating that my colleagues in Congress are so afraid of the gun industry that they pretend there aren't public policy responses to this epidemic. There are, and the thoughts and prayers of politicians are cruelly hollow if they are paired with continued legislative indifference. It's time for Congress to get off its ass and do something," he said.
Murphy has previously pushed for more extensive gun control laws. Last year, he mounted one of the longest filibusters in history, nearly 15 hours, while pushing for a gun control vote in the wake of the Orlando Pulse terrorist attack. Murphy formerly represented the district of Newtown, Connecticut, where 20 children and six others were killed in a 2012 school shooting.