WASHINGTON — Investigators have spent most of this week piecing together the story of Stephen Paddock, who on Sunday opened fire from his Las Vegas hotel suite, gunning down 58 people at a country music festival and injuring hundreds more.
They have explored a web of clues, delving into Paddock’s gun purchases, computers, and travel plans, and speaking with his relatives and girlfriend. What they lack, however, are answers.
On Friday, the fifth full day of the investigation, the biggest remaining question about the shooting remained unanswered: Why did Paddock, a 64-year-old avid gambler, meticulously plan and carry out the deadliest mass shooting in modern American history?
Unlike many other mass killers who have unleashed bloodshed in America’s churches, colleges, nightclubs, workplaces, college towns, or public spaces, Paddock left no clear sign that authorities have identified so far.
After previous mass shootings, there were bigoted screeds posted online, confessions to police, videotaped rants, histories of violent behavior, or worrisome trails of arrest records and mental health consultations.
Here, instead, there is mystery. People who knew Paddock described him as antisocial, someone who went out of his way to avoid other human beings, but his girlfriend said she saw no indication that he was capable of such horror.
Other questions still surrounded the shooting, as Joseph Lombardo, the Las Vegas sheriff, outlined during a news briefing.
Did anyone help Paddock or know of his plans? Did Paddock intend to die in his hotel suite — shooting himself before a SWAT team breached the door on Sunday night — or had he hoped to escape? What, if anything, did it mean that he had intensified his gun-buying habits in the year before the shooting?
‘‘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,’’ Lombardo told reporters. ‘‘Anything that would indicate this individual’s trigger point and would cause him to do such harm, we haven’t understood it yet.’’
FBI agents are piecing together Paddock’s life in the weeks and months before the massacre, hoping to unearth an explanation. Aaron Rouse, the special agent in charge of the FBI’s Las Vegas division, warned that the inquiry will ‘‘take a while,’’ but he pledged that authorities ‘‘will get to the bottom of this no matter how long it takes.’’
The Clark County coroner in Nevada on Thursday formally identified the 58 people killed in the massacre. Their names and stories have already emerged, tales of people gunned down while next to their friends and relatives.
Of the 58 people killed during the massacre, 36 were women and 22 were men. The youngest victim, Bailey Schweitzer, was 20; the oldest, Pati Mestas, was 67.
The rampage also sent nearly 500 people to the hospital, many with gunshot wounds. Others were injured during the frenzied attempts to flee the carnage. More than two dozen of those still hospitalized as of Thursday remained in critical condition.
As Paddock’s background has come into focus, the portrait that emerged was one of a financially well-off man who disliked being around other people and sought to avoid speaking with them.
Paddock would buy apartments, move into them to keep an eye on his investment, but ‘‘still would employ other people to talk to the tenants because he didn’t want to talk to the tenants,’’ said a real estate broker who helped Paddock sell multiple properties in California more than a decade ago.
Paddock’s aversion to human contact, the real estate broker said, was in part why he preferred playing video poker, a type of gambling that doesn’t require interaction with other players.
Paddock had expressed a dislike for taxes and the government, the broker said, even selling off several buildings in California to move his money to the low-tax havens of Texas and Nevada. A person familiar with the investigation into the massacre said these antigovernment views alone didn’t explain why Paddock targeted a country music concert.
Before ascending to the 32nd floor of a Las Vegas hotel and opening fire on 22,000 concertgoers far below, Paddock had booked space in two other hotels overlooking popular music festivals — one in Las Vegas last month and the other in Chicago a month earlier.
Investigators were unsure of the significance of the hotel bookings and are trying to determine if they were ominous signs of the horror to come or the meaningless actions of a man with the financial means to fly around the country.
Two months before he opened fire from the Mandalay Bay Resort and Casino, targeting a country music festival far below, Paddock had made a reservation at a high-rise hotel overlooking Lollapalooza, a music festival in Chicago’s Grant Park, according to two people familiar with the investigation.
From the Blackstone Hotel, where Paddock had made the reservation, a person with the right room could see clear across Lollapalooza and to Lake Michigan, which runs along the park’s eastern side.
Instead, Paddock headed toward Las Vegas, home to so many of the casinos where he felt at home. Paddock was known to sit for hours playing video poker and slot machines, gambling with tens of thousands of dollars and earning VIP status.
Paddock arrived at the Mandalay Bay on Sept. 28, three days before the concert shooting, bringing with him 23 guns, a dozen of them equipped with ‘‘bump stocks,’’ which allow for more rapid fire.
Paddock also had in his car thousands of rounds of ammunition he never fired, along with explosive material, including fertilizer used to make bombs and Tannerite, a substance used in explosive rifle targets. More guns, ammunition, and explosive material were found at his homes, police said.