Investigators previously said that the security guard was shot after Paddock had already spent 10 minutes firing into the crowd of concertgoers gathered below the hotel. Paddock killed 58 people and injured more than 500 before killing himself.
Although Campos had radioed for police to come after the exchange, police officers found him "in the hallway" as they rushed to the shooter's room, Lombardo said.
The sheriff also said investigators do not believe that a single event pushed him to do what he did.
"Mr. Campos was encountered by the suspect prior to his shooting to the outside world", Lombardo said at a Monday news conference.
The "Welcome to Las Vegas" sign is surrounded by flowers and items, left after the October 1 mass shooting, in Las Vegas, Nevada U.S. October 9, 2017. Paddock apparently detected Campos via surveillance cameras he set up outside his hotel suite, police have said.
Police are now looking to speak to any escorts who Paddock may have been with in the days before the massacre took place.
Las Vegas police officer David Newton told CBS News program "60 Minutes" on Sunday that he entered the room and saw a note on the shooter's nightstand with numbers that appeared to be created to help his aim.
Investigators are still trying to piece together key components of the massacre, including Paddock's motivation for planning such a horrific assault. The room was crowded with weapons and his vehicle packed with explosives.