Campos was shot while investigating an alarm that was unrelated to Paddock's room.
Friends and family held a candlelight vigil in Placentia for 38-year-old Nicol Kimura on Sunday evening - a week after the mass shooting.
USA police have revealed new details on the timeline of the deadliest shooting in United States history, which happened in Las Vegas on Sunday, October 1. Law enforcement made a significant change to the timeline of the mass shooting, calling into question whether gunman Stephen Paddock could have been intercepted sooner.
A note containing handwritten numbers for wind, trajectory, and distance was discovered by Steven Paddock's body inside the Las Vegas hotel room where he took his life last Sunday after slaughtering 58 people and injuring hundreds, officials have confirmed.
At the news conference Monday, Lombardo said Campos, after he was shot on October 1, "immediately" told security what happened. "Because this individual purposefully hid his actions leading up to this event and it is hard for us to find answers for those actions". Six minutes later, Paddock began firing into the crowd at the Route 91 Harvest Festival, authorities said.
Mr Lombardo said security guard Jesus Campos was in a hallway of the Mandalay Bay hotel responding to a report of an open door when he heard drilling from Paddock's room. The initial reports that night of multiple shooters at several hotels would also have confused police, he added.
"I'm frustrated", Joseph Lombardo, the Las Vegas sheriff, said at a news briefing. Campos alerted security of the situation, Lombardo said, but police hunting for the gunman were not aware of the shots fired at the guard.
The president of the union that represents Campos and officials with MGM Resorts International, which owns the Mandalay Bay, could not be reached for comment.
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".
Las Vegas Metropolitan Police Department spokesman Aden Ocampo-Gomez said the office will respond later to questions involving police response time to the shooting that killed dozens of people at an outdoor concert.
Similar exercises have followed high-profile mass shootings across the country, including those in San Bernardino, California, and at the Washington Navy Yard.
Police still have not determined Paddock's motive in the attack. "And I don't know what happened to him", she said during an emotional interview.
Sources also said that the gunman's gambling wages went up during that time, and he completed computer searches where he was looking at a lot of different hotel venues - some apparently just to research, some of which he actually traveled to.
"Our officers got there as fast as they possibly could and they did what they were trained to do", assistant sheriff Todd Fasulo said.
Paddock opened fire on a country music event on the Las Vegas Strip from a hotel room at The Mandalay Bay before turning a gun on himself. Authorities had previously said they believed Campos drew Paddock's attention away from firing out the window, and that Paddock didn't fire any further shots after wounding the guard.
At 10:05 p.m., the Las Vegas Strip's bright lights dimmed for about 10 minutes to mark the passing of exactly a week since a gunman opened fire, killing 58 people and wounding nearly 500 at a country music festival.
"It isn't because nobody is not doing their job", he said.
Bump stocks have become the focus of controversy since the shooting, and a prominent gun-control group on Tuesday filed a lawsuit against a manufacturer of these devices. When they arrived on the 32nd floor at 10:17 p.m., Campos told them that he was shot and directed them toward Paddock's room.