As investigators tried to piece together the reason why a man with an arsenal of rifles rained deadly fire down on Las Vegas concertgoers, dozens of his victims remained in the hospital.

At Sunrise Hospital, where 200 of the killed, wounded and hurt were taken Sunday night, 45 people are still hospitalized, about half of them in critical condition, according to the medical center's most recent update.

And it appears gunman Stephen Paddock was not just shooting at people when he killed 58 country music lovers at a festival near the Mandalay Bay hotel.

A large fuel tank at nearby McCarran International Airport was hit by two bullets, one penetrating the outer shell, officials said on the airport's Facebook page.

But there never was any danger, officials said.

"There is almost zero likelihood gunfire damage could trigger a fire or explosion at a commercial fuel storage facility," the Facebook post said.

There were several vigils held at twilight in Las Vegas on Thursday, including one for Officer Charleston Hartfield, who was off-duty and attending the concert when he was killed. Hundreds of people came to Police Memorial Park to honor his memory.

There is still much mystery surrounding Paddock, a 64-year-old retired accountant from Mesquite, Nevada, who liked to gamble in Vegas casinos and had more than 40 guns in two homes and his hotel suite.

Did he want to escape?

Chilling clues revealed by police suggest the man behind the deadliest mass shooting in modern US history planned to inflict even more carnage.

Paddock didn't just have 23 weapons in his hotel suite, which he turned into a sniper's nest.

He also had more than 50 pounds of explosives and 1,600 rounds of ammunition in his car in the hotel parking lot, police said.

Investigators think Paddock intended to survive the massacre, Las Vegas police Sheriff Joseph Lombardo said.

"He was doing everything possible to see how he could escape," Lombardo said, declining to detail specifics.

But what motivated Paddock to kill dozens of strangers and whether he had help remains a mystery.

Law enforcement officials who have been briefed on the investigation told CNN on Thursday they have seen no indication that Paddock had an accomplice or that anyone was aware of his planning.

Law enforcement analyst: Car bomb possible

Of the explosives found in Paddock's car, authorities first found several pounds of ammonium nitrate, Lombardo said.

He said a later search of cases found in the car revealed 50 pounds of Tannerite -- a brand-name product that's marketed as explosive rifle targets.

The cache of explosives in Paddock's car could indicate plans for a car bomb, CNN law enforcement analyst Art Roderick said.

"Those explosives, that's the scary part. What was he going to do with those? I mean, you don't just acquire them and leave them in your vehicle and not have a plan for them," said Roderick, former assistant director of the US Marshals Service.

"The Tannerite could have set off the ammonium nitrate," Roderick said. "So, was he using that as a vehicle-borne explosive device?"

It's possible no one will ever learn Paddock's plan for the explosives. The gunman killed himself before police breached his hotel room door.

Booking rooms near other music festivals

Before checking into Mandalay Bay days before the massacre, Paddock rented a room at a Las Vegas condo complex that overlooked another music festival.

Paddock rented the room at the Ogden condo complex via Airbnb during the Life is Beautiful music festival, which lasted from September 22 to 25, the sheriff said.

"Was he doing pre-surveillance? We don't know yet. This is all conjecture at this point," Lombardo said.

Security 'top priority' for concert, festival organizers following Vegas massacre

And 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 Thursday that it was the shooter Stephen Paddock who booked the room at the Blackstone Hotel.

Wagstaff Worldwide said Blackstone Hotel is cooperating with authorities.

Victim in a coma

Tina Frost, 27, is one of those victims still in critical condition.

She was at the Route 91 Harvest festival with her boyfriend and other friends when she was shot near one of her eyes. She has been in a coma for four days.

"She has her whole life in front of her, and with one incident, we have a nightmare," her mother, Mary Moreland, told CNN.

Frost was among the victims saved by a stranger who carried her through the carnage to a pickup truck.

An online fundraiser has accumulated almost $400,000 for Frost's medical bills.

"I'd throw it all away to have my daughter back," Moreland said. "It's overwhelming."

A new timeline

New evidence shows Paddock fired his first shots into the Route 91 Harvest music festival at 10:05 p.m. Sunday -- three minutes earlier than what police previously reported, Lombardo said.

For 10 minutes, Paddock sprayed hundreds of bullets into the crowd about a quarter mile away. The shots pummeled the gathering of 22,000 people with devastating speed, due to the help of bump stocks -- legal accessories that make weapons fire similarly to an automatic rifle.

As the indiscriminate killings continued, police said, cameras were positioned inside and outside Paddock's hotel suite and in the door's peep hole.

A security guard approached the 32nd-floor suite and was shot in the leg by Paddock. The gunman fired "well over 200 rounds" into the hallway, Lombardo said.

"It's amazing that security guard didn't sustain additional injury," the sheriff said.

At 10:15 p.m., Paddock fired his last shots, police said. Three minutes later, a security guard told Las Vegas police he'd been shot and directed officers to the gunman's room.

More than an hour later, at 11:20 p.m., police first breached Paddock's suite and found his body on the ground. Seven minutes later, officers gained access to a second room of the suite. No one else was found, and police declared the suspect "down."

The elusive motive

As more than 100 investigators dig for answers, police aren't sure what turned Paddock into a mass killer.

"What we know is Stephen Paddock is a man who spent decades acquiring weapons and ammo, and living a secret life, much of which will never be fully understood," the sheriff said.

Investigators said something may have happened to Paddock between October 2016 and last month that compelled him to purchase more weapons. Paddock bought 33 guns, mostly rifles, during that period, an ATF spokesperson said.

A note was found in Paddock's Mandalay Bay hotel room, but it was not a suicide note, the sheriff said. He did not detail what the note said.

No evidence indicates terrorism, FBI special agent Aaron Rouse said, but the investigation is ongoing.

Why officials aren't calling the Las Vegas massacre 'domestic terrorism'

Girlfriend: He sent me to the Philippines

Investigators want to know whether Paddock's girlfriend, Marilou Danley, has information that can explain what sparked the massacre.

Danley flew Tuesday to Los Angeles from the Philippines and has been cooperating with authorities, Rouse said.

Danley, through her attorney, said that she didn't know Paddock planned to carry out a mass shooting.

He bought her a ticket to the Philippines about two weeks ago, then wired her money so she could buy a house there, she said in a statement. At the time, she worried he was trying to break up with her, she said.

Paddock wired $100,000 to the Philippines, a law enforcement source said. The FBI is working with Philippine authorities to get more details.

"It never occurred to me in any way whatsoever that he was planning violence against anyone," Danley said in the statement. "I will cooperate fully with their investigation. Anything I can do to help ease suffering and help in any way, I will do."

The hunt for possible accomplices

Authorities are investigating whether Paddock acted alone or had accomplices. Lombardo, the sheriff, 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.

Police didn't hold a media briefing Thursday. Many officials were at the vigil for Officer Hatfield.

CORRECTION: An earlier version of this story gave an incorrect time frame for when Paddock acquired 33 firearms. It was roughly 11 months.

CNN's Brad Parks, Joe Sutton, Sheena Jones, Janet DiGiacomo and Dan Simon contributed to this report.

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