The high-powered guns were scattered around the room on an upper floor of the Mandalay Bay Resort and Casino in Las Vegas. One of the firearms, a rifle outfitted with a scope, was near a window, its barrel pointed toward the popular Vegas Strip.

But this was 2014, three years before Stephen Paddock used a suite on the 32nd floor of the Mandalay Bay to stock an array of guns and carry out the deadliest mass shooting in modern American history, killing 58 people and injuring hundreds of others at a country music festival.

That first room with the rifle next to the window had been occupied by a felon, Kye Aaron Dunbar, who, like Mr. Paddock, had brought the guns upstairs in baggage.

The Dunbar case, which attracted little public attention at the time, is now being raised by lawyers for victims of last year’s massacre who are suing MGM Resorts International, owner of the Mandalay Bay, for negligence. For Mr. Paddock’s victims, the Dunbar case shows that the hotel did not do enough to prevent guests from bringing an arsenal of weapons to the hotel, and that the tragedy that unfolded one year ago was foreseeable.