A few minutes later, Paddock began raining down bullets for 10 minutes in an attack that killed 58 people - the deadliest mass shooting in modern USA history, Lombardo said.
Police released few details about the new timeline and did not respond to questions from the Associated Press, including whether anyone from the hotel called 911 to report the hallway shooting.
"This individual purposely hid his actions leading up to this event, and it is hard for us to find the answers", said Lombardo, who agreed he was frustrated with the speed of the investigation.
The Las Vegas Police Department's K-9 unit, said he noticed the paper on the shooter's nightstand, not far from one of the windows Paddock had smashed with a hammer before firing into the unsuspecting crowd below with high-powered semi-automatic rifles.
Charles "Sid" Heal, a retired Los Angeles County sheriff's commander and tactical expert, said the new timeline "changes the whole perspective of the shooting". By the time officers entered the room, Paddock was dead from a self-inflicted gun shot wound, CNN reported.
Federal investigators returned to search the home of Paddock on Sunday, while the officers who raided his hotel room door the night of the shooting gave a harrowing account of a barricaded door they had to bust through and the booby-traps they feared they'd find.
Lombardo said police and Federal Bureau of Investigation agents, including behavioral profilers, still haven't found a particular event in Paddock's life that might have triggered the shooting.
"As I've said from day one, we want to figure out the why to this and we'd like to know the motive".
Aldean's wife, Brittany, posted a picture of herself and Jason on Instagram looking at the Mandalay Bay resort, where shooter Stephen Paddock opened fire on the crowd from his hotel room October 1.
Lawn chairs, baby strollers, cowboy hats, boots and thousands of other items were discarded as 22,000 people fled the concert venue while bullets flew from the Mandalay Bay hotel casino across Las Vegas Boulevard.
"Currently, we do not believe there is one particular event in the suspect's life for us to key on", the sheriff said. In addition, Campos prevented a maintenance worker on the same floor from receiving any injuries, the sheriff said.
"They weren't aware of him being shot until they met him in the hallway after exiting the elevator", Lombardo said Monday.
"We do not know whether he had planned to cause additional harm outside of what happened at Mandalay Bay", Lombardo said.
Sgt Bitsko said: 'Initially, I was thinking, "This is a booby trap, it's going to explode". "They are minute changes".
Law enforcement authorities on Monday made a significant change to the timeline of the Las Vegas mass shooting, saying the gunman shot a hotel security guard before he opened fire on concert-goers.
When the gunfire stopped, officers said they stood behind the door with only a single police shield for protection and prepared to blow down the door with explosives. "And then you have the flashing lights", Newton said.
"Stacks and stacks of magazines everywhere. It just looked like nearly a gun store", he said.
The suite smelled of gun powder and its floor was littered with shell casings, the officers said.
And why did Paddock stop firing?
The Las Vegas Review-Journal reports (http://bit.ly/2yzrWEz) that Eric Paddock arrived in town Saturday for hours of interviews with Federal Bureau of Investigation agents, a police detective, a profiler and a psychologist.
"I could see on it he had written the distance, the elevation he was on, the drop of what his bullet was gonna be for the crowd", Newton said.