No shots were fired in the final assault, and police denied initial reports that SWAT officers rappelled down Harrah's hotel-casino and crashed through the window during an assault on room 2036.
"We were forced to take out an outside window in our attempts to take him into custody," police Sgt. Chris Jones said. He described shattering the window on the 29-story tower as a tactical diversion.
Guests were evacuated from several nearby floors, but the casino remained open during the standoff.
The gunman shot into the hallway as police and paramedics arrived during the initial hectic minutes, Jones said. The victim was pronounced dead later at a hospital.
The suspected gunman also shot out of the room as SWAT officers got in place for the standoff and assault, Jones said, adding there were clear signs of a struggle between the gunman and the man who died after the original shooting.
Police fired no shots during the initial encounter with the gunman, during the standoff or during the assault on the 20th floor, Jones said.
Guests in sleep clothes and robes were evacuated from the 19th, 20th and 21st floors and offered blankets and food at the hotel buffet, Harrah's spokesman Alberto Lopez said.
Jim Hack, 31, a stockbroker from Phoenix, said he heard two gunshots about 12:30 a.m., opened his door and saw a man in his mid-30s bleeding in the hallway several rooms away.
"He was crying for help and he was having trouble breathing," said Hack, who said he closed his door and called security while the wounded man pleaded for someone to pull him into an adjacent room.
The gunman and the dead man were identified as guests at the 1,275-room hotel, but their names were not immediately made public.