LAS VEGAS — Read the latest on the Las Vegas shooting with Thursday’s live updates.

When Stephen Paddock pulled his car up to the wide circular driveway at the Mandalay Bay Resort and Casino, a half-dozen bellboys and valets were likely to be there to help. When he walked past the two giant stone lions and through the glass doors into the lobby, greeters would probably have ushered him the roughly 50 steps to the wooden doors with frosted glass where high rollers check into the hotel.

When he emerged and walked another 50 feet to the elevator bank, dozens if not hundreds of guests and employees may have passed him. Once on the 32nd floor, he would have walked down a long hallway to his suite, with its minibar, sofas and large bedroom. There, he would have started to unpack some of the 10 suitcases he brought to the hotel, containing the guns that he would use to commit mass murder.

Mr. Paddock appeared to have little trouble bringing nearly two dozen weapons and thousands of rounds of ammunition into his suite at the Mandalay Bay. The hotels and the casinos connected to them, not just in Las Vegas but around the country, are designed to welcome visitors and make it as easy as possible for them to relax and spend money.

Now, hotels, casinos and law enforcement agencies are confronting their security vulnerabilities and trying to figure out what more they can and should do to prevent attacks like the mass shooting in Las Vegas.

Short of installing metal detectors at all the many entrances, or individually searching arriving bags, though, it may be nearly impossible to prevent visitors from carrying weapons into facilities like the Mandalay Bay, security experts say.

“Because of the open nature of casinos and hotels, it’s almost impossible to do the search you do at an airport,” said Ed Davis, who was the police commissioner in Boston during the Boston Marathon bombing and is now an adviser to the American Gaming Association, the casino industry group. “Unfortunately, Las Vegas is a big soft target,” Mr. Davis said, “and the fact that it hasn’t happened here before is a miracle.”