Las Vegas shooter Stephen Paddock tried to buy tracer ammunition at a gun show in the Phoenix area in recent weeks, a law enforcement official briefed on the investigation tells CNN.
Paddock bought other ammunition at the show, but he couldn't obtain the tracer ammunition because the vendor didn't have any to sell, the official said.
As a result Paddock, who killed 58 people and injured hundreds of others in Sunday's deadly attack, probably couldn't see what he was hitting in the darkness, the official said -- he was indiscriminately spraying bullets into the crowd just hundreds of yards from his suite on the 32nd floor of the Mandalay Bay hotel.
The official explains that tracer ammunition, which is legal, would have allowed him to see and perhaps be more accurate.
In addition to the 23 weapons in his hotel suite, which he turned into a sniper's nest, Paddock had more than 50 pounds of explosives and 1,600 rounds of ammunition in his car in the hotel parking lot, police said, fueling suspicion that he intended to survive the massacre.
"He was doing everything possible to see how he could escape," Las Vegas Police Sheriff Joseph Lombardo said, declining to detail specifics.
Authorities: Paddock acted alone
After speculation that Paddock had outside help in perpetrating the shooting spree, authorities said there is nothing to suggest he had help.
Law enforcement officials briefed on the investigation told CNN they have seen no indication so far that Paddock had an accomplice or that anyone was aware of his attack planning.
Lombardo, the sheriff, had previously expressed skepticism that the gunman carried out his plan by himself.
"Do you think this was all accomplished on his own? You've got to make the assumption he had to have some help at some point," he said.
As the investigation grinds on, Las Vegas Metropolitan Police Department officers led the funeral of LVMPD officer Charleston Hartfield Thursday, who was among those gunned down at the Route 91 Harvest Festival country music event.
After escorting his body to Palm Downtown Mortuary and Cemetery, a memorial was held for the slain police officer at Police Memorial Park in the northwest of the city -- one of several vigils held at twilight in Las Vegas on Thursday.
Gun debate continues
Elsewhere, in the wake of the deadly attack, the Eastside Cannary Casino Gun Show that was expected to be held in Las Vegas this weekend has been canceled, David Strow of Boyd Gaming Corporation tells CNN.
"This was a mutual decision with the show's organizers, given recent events, it was the prudent thing to do," Strow said.
Four days after the mass shooting, authorities are still trying to determine the motivation of the retiree, who had no criminal record and did not raise any flags while purchasing an arsenal of weapons, some modified to act like automatic rifles.
In the aftermath of the shooting, pro-gun Republican lawmakers and the National Rifle Association (NRA), the powerful pro-gun lobby, have suggested supporting a review of "bump stocks," modifications to semi-automatic rifles, which allow the shooter to fire rounds more rapidly.
Politicians from both sides of the aisle and lobbyists are now saying the controversial devices, which sell for under $200, should be subject to additional regulation.
US President Donald Trump is open to considering legislation that would ban bump stocks but wants to hear more information on the matter before making a final determination, the White House said Wednesday.
'Numbers' found on note
Lombardo said a note with numbers written on it was found in Paddock's room, according to the New York Times. Authorities are trying to analyze its meaning, but Lombardo didn't elaborate on whether they are significant or not.
"Lombardo said that it contained numbers that were being analyzed for their relevance, and that it was not a manifesto or suicide note," the Times reported.
Paddock had rented rooms at other festivals
Before checking into the Mandalay Bay days before the massacre, Paddock rented a room at a Las Vegas condo complex that overlooked the Life is Beautiful music festival.
In addition, in August, a person named Stephen Paddock reserved a room at Chicago's Blackstone Hotel during the city's Lollapalooza music festival, said Wagstaff Worldwide, which represents the hotel.
But that person never checked into the hotel, which overlooked the festival, Wagstaff Worldwide spokeswoman Emmy Carragher said.
It was not immediately clear whether the Stephen Paddock who booked the room was the same Stephen Paddock behind the Las Vegas massacre.
The Chicago Tribune, citing an anonymous law enforcement source, reported that it was the shooter Stephen Paddock who booked the room at the Blackstone Hotel.
Hairdresser: Paddock spoke about girlfriend's trip
Kallie Beig, who worked at the Great Clips in Mesquite, Paddock's hometown, told CNN exclusively that she had cut Paddock's hair at least three times over the past three years, and that every time he had come in, always early in the morning, he had smelled of strong liquor.
He would tell her that he'd been up all night gambling, she said.
The last time she saw him was two months before Sunday's tragedy, she said.
During his last visit, he told her he was planning on sending his girlfriend, Marilou Danley, to the Philippines and he was going to be alone. She did not discuss the trip with Danley personally.
"The last time I saw him was probably only about two months ago... he came in and got his hair cut, and again, smelled of alcohol, and his girlfriend was with him... doing her own thing, and he was telling me about her leaving to go to the Philippines."
She said that the interaction was normal and didn't raise any red flags with her.
"He was going to be home alone hanging out for a while by himself but it wasn't anything weird, it wasn't anything that seemed off."
In her statement released through her attorney, Matt Lombard, Danley said the trip was a surprise.
"A little more than two weeks ago, Stephen told me he found a cheap ticket for me to the Philippines and that he wanted me to take a trip home to see my family," she said.
"Like all Filipinos abroad, I was excited to go home and see family and friends."
Beig characterized their relationship as quite cold and distant -- she said she didn't see them interacting in any sort of intimate way.