Stephen Paddock's massive arsenal raises questions about gun regulation and hotel security.
"The crime that took the lives of dozens of civilians is shocking in its cruelty," Putin said in a telegraph sent to President Trump.
Democratic Representative Seth Moulton of Massachusetts said he took the same stance following the Orlando mass shooting.
The shooting, which left 59 dead and 529 more injured, is the deadliest in recent U.S. history.
"This attack has created a public health and medical emergency in Clark County and the surrounding areas," the governor's executive order states.
O'Reilly, a former Fox News host, claimed gun control laws wouldn't prevent mass shootings such as those in Las Vegas.
"He never gave any indication or reason to believe he was unstable or unfit at any time," one store owner said in a statement.
Joe Lombardo said there was nothing to alert authorities to shooter Stephen Paddock.
Representative Al Green says it's time for the nation to focus on mourning the shooting victims.
Brett Kenyon lived through the Sandy Hook shooting near his hometown in Danbury, Connecticut. Then, Sunday, he was at work in the Cosmopolitan of Las Vegas, when the worst mass shooting in U.S. history took place.
"I am stunned by the level of trauma Congress is willing to make us suffer through," she said.
Patrick Benjamin Paddock, also known as Benjamin Hoskins Paddock, was wanted for bank robberies, according to newspaper accounts.
Gun share prices rise after mass shootings with the perception that tighter gun control rules will follow and that people need to better protect themselves.
The attack that left more than 50 people dead in Las Vegas meets Nevada's definition of an "act of terror."
There is little chance of movement on guns while the GOP controls the House, Senate and White House.
Police have identified a single attacker in the incident in which more than 50 people were killed.
The gunman, Stephen Paddock, had at least 19 rifles and handguns and fired hundreds of rounds of ammunition from his hotel room at the Mandalay Bay hotel.
The four deadliest mass shootings in the U.S. occurred in the past 10 years.
"Are we really prepared to say that we're powerless in the face of such carnage, that the politics are too hard?" Obama said after Sandy Hook. Trump agreed.
In August this year, Nevada voted narrowly in support of Question 1 for background checks on private gun sales.