Las Vegas police have chased "more than 1,000 leads" in their quest to establish a motive for why a gunman killed 58 people at a music festival.
Survivors are still reeling five days after Stephen Paddock, 64, opened fire from his hotel room on the crowd below before turning the gun on himself.
The attack is considered the deadliest mass shooting in recent US history.
Police said they have "looked at everything" but have yet to determine why Paddock went on a shooting rampage.
"We have looked at everything, literally, to include the suspect's personal life, any political affiliation, his social behaviours, economic situation, and any potential radicalisation that so many have claimed," said Kevin McMahill, undersheriff of the Las Vegas Metropolitan Police Department.
But as police continue to piece together the clues left behind by the elusive gunman, several questions remain unanswered, including why the the wealthy, retired accountant carried out such a crime.
Las Vegas Metropolitan Police Department Sheriff Joseph Lombardo said police are examining a computer and multiple electronic devices found in Paddock's Mandalay Bay suite as well as evidence taken from his homes in Mesquite and Reno, Nevada.
Investigators also found a note containing numbers inside the hotel suite, but police say it was not a suicide note or manifesto.
He is not believed to have held any extremist views and did not call police to explain his actions like Omar Mateen, the Orlando nightclub gunman who fatally shot 49 people last year.
Authorities have revealed few details about what has been discovered and whether any of it contains clues as to he carried out such an attack.
Andrew McCabe, the deputy director of the FBI, conceded on Wednesday the case was "somewhat different than many of the ones we've dealt with in the past".
Paddock amassed a cache of weapons over the last 13 months, purchasing a haul of 33 guns, some of which had been modified with bump-stocks, or devices that enable guns to operate like fully automatic weapons.
He smuggled into the hotel 24 weapons and thousands of rounds of ammunition, concealed in 10 suitcases, for the "meticulously planned" attack, police say.
But Paddock may have been scouting other locations, including the Life is Beautiful music festival, which was held in Las Vegas the weekend before Sunday's attack.
The gunman booked a luxury unit in the Ogden, a high-rise building that towered over the open-air concert, which featured acts including Muse, Lorde and Chance the Rapper.
US media reports now say the suspect may have considered other festivals, including Chicago's Lollapalooza, a massive August festival attended by hundreds of thousands of people.
He also researched hotels near Boston's Fenway Park and the Boston Center for the Arts, the city's police commissioner William Evans said on Friday.
In a press conference on Wednesday, Sheriff Joseph Lombardo said he saw evidence that Paddock had planned to escape after the attack, but declined to elaborate. Paddock instead turned the gun on himself as police stormed his suite.
Adam Lankford, a University of Alabama criminologist and researcher who tracks global mass shootings, told the BBC he believes any evidence of an escape plan was probably a fantasy.
He pointed to Eric Harris and Dylan Klebold, two teenage gunmen who killed 12 students and a teacher at a Colorado high school before killing themselves in 1999, who fantasised about a second attack.
Harris detailed his plot in a journal and suggested the two would hijack a plane and crash it into New York City if they survived the school shooting - an escape fantasy, Mr Lankford said.
Mr Lankford also noted the bunker that Paddock created in the hotel room, which he outfitted with surveillance cameras to see anyone approaching.
"You set up the cameras so you aren't caught alive," Mr Lankford said.
Paddock also had in his car more than 50lbs of exploding materials, 1,600 rounds of ammunition and fertiliser, which can be used to make explosives, which could signal a plan to flee.
But he also purchased a plane ticket for his girlfriend to travel to her native Philippines and wired her $100,000 (£75,400) before the shooting rampage, which some experts say could suggest he was trying to ensure she was taken care of after his death.
Police have questioned Paddock's girlfriend, Marilou Danley, who has co-operated with police since she returned home from the Philippines earlier this week.
Ms Danley, 62, said she had no idea about what Paddock had been plotting, adding that she thought the money was a sign he was planning to end the relationship.
Eric Paddock, the suspect's brother, told reporters that his brother did not have any ties to political or religious groups.
Sheriff Lombardo has previously suggested that investigators were open to the possibility that someone else was involved.
When asked if he had an accomplice, Mr Lombardo said he had the "assumption that he had to have some help at some point".