WARNING: GRAPHIC CONTENT - Las Vegas Metropolitan Police have released bodycam footage from officers who responded to the mass shooting at the Route 91 Harvest Festival.
It comes as the girlfriend of the gunman who killed 59 people on the LasVegas Strip is being questioned by police after returning to the US from the Philippines.
Sheriff Joseph Lombardo said investigators are hoping to get some insight from Marilou Danley on why Stephen Paddock opened fire on a concert crowd from a high-rise hotel room.
Ms Danley had been out of the country for weeks before the shooting but had been named as "a person of interest".
A law enforcement official said she arrived late on Tuesday night on a flight from Manila in Los Angeles, where FBI agents were waiting for her.
On Wednesday, President Donald Trump was due to visit LasVegas to meet public officials, first responders and some of the 527 people who were injured in the attack.
Earlier investigators said Paddock had planned the massacre so meticulously that he set up a camera in the peephole of his hotel room in an apparent attempt to spot anyone coming for him.
He also transferred 100,000 US dollars (£75,000) overseas just days before the massacre.
The 64-year-old, from Mesquite, Nevada, sprayed bullets on revellers enjoying the Route 91 Harvest Festival from the 32nd floor of the Mandalay Bay Hotel and Casino.
He killed himself before officers stormed Room 135 in the gold-coloured glass skyscraper.
Sheriff Lombardo said he is "absolutely" confident investigators will establish why the big-spending gambler carried out the attack - the deadliest mass shooting in modern US history.
The cameras Paddock set up at the Mandalay Bay hotel were part of his extensive preparations that also included stockpiling nearly two dozen guns before the attack.
"I anticipate he was looking for anybody coming to take him into custody," Mr Lombardo said.
"The fact that he had the type of weaponry and amount of weaponry in that room, it was pre-planned extensively, and I'm pretty sure he evaluated everything that he did and his actions, which is troublesome."
Undersheriff Kevin McMahill told reporters that Paddock also set up two cameras in the hallway outside his room so he could watch for anyone approaching.
He said Paddock fired on and off for nine to 11 minutes and unleashed about a dozen volleys. The first call about shots fired came in at 10.08pm and the gunfire stopped at 10.19pm.
In addition to the cameras, investigators found a computer and 23 guns in the hotel room. Officials said Paddock had devices attached to 12 weapons that allow semi-automatic rifles to mimic fully automatic gunfire.
Nineteen more guns were found at Paddock's Mesquite home and seven at his Reno house.
Investigators are still trying to trace the 100,000 US dollars (£75,000) Paddock transferred to the Philippines in the days before the shooting, and are also looking into a least a dozen reports over the past several weeks that said he had gambled more than 10,000 dollars per day, a US official said.
More than 500 people were injured in the rampage, some by gunfire, some during the chaotic escape. At least 45 patients at two hospitals remained in a critical condition. All but three of the dead had been identified by Tuesday afternoon.
Country music star Jason Aldean was performing on Sunday night at the end of the three-day festival in front of a crowd of more than 22,000 when the gunman opened fire from inside the 44-floor hotel across the street.
He has since cancelled three forthcoming tour dates out of respect for the victims and to take time to mourn.