The mystery and motive behind mass killer Stephen Paddock — gambler, accountant, auditor and real estate investor — continues to baffle federal authorities and law enforcement officials in Las Vegas who were working on Wednesday to discover what drove the 64-year-old to commit the worst mass murder in modern U.S. history.

Police body camera video released Tuesday night revealed the sheer chaos at the Route 91 Harvest Music Festival on Sunday, when a gunman opened fire from the 32nd floor of the Mandalay Bay Resort and Casino, killing 58 people and injuring more than 480 others. The video showed people screaming and scrambling as officers tried to figure out the location of the gunman and shuttle people to safety.

According to those who knew him, Mr. Paddock showed no signs of mental illness, extreme political views or an unhealthy interest in guns prior to the massacre.

However, Mr. Paddock was prescribed anti-anxiety medication during the summer and purchased 50 10-milligram tablets of diazepam, better known under its brand name Valium, on June 21, the Las Vegas Review-Journal reported, citing records from the Nevada Prescription Monitoring Program.

According to media reports, Mr. Paddock liked to gamble, had homes in Southern California, Texas and Nevada, had plenty of money and held a succession of steady jobs as a mail carrier, accountant, auditor and apartment manager, according to media reports.

In an era when social media invites full-throated expression of even the most minor annoyance, Mr. Paddock gave no hint of whatever it was that drove him check into the hotel suite with 23 high powered weapons with scopes, smash out two windows and unload on 22,000 concertgoers at a country music festival below.

Several new details emerged Tuesday about Mr. Paddock and how he worked methodically to thwart law enforcement. As he fired round after round starting at 10:08 p.m. and lasting for 11 minutes, video cameras he set up at the hotel door’s peephole and outside in the hall kept an eye out for police storming the room, according to Clark County Sheriff Joe Lombardo.

“It was preplanned, extensively, and I’m pretty sure that he evaluated everything that he did in his actions, which is troublesome,” Sheriff Lombardo said.

Mr. Paddock shot through his hotel door, hitting a security guard in the leg before police got into to the room to find him dead from a self-inflicted gunshot wound.

Mr. Paddock had no criminal history. And despite repeated claims by the Islamic State to the contrary, he also had no ties to international terror groups, authorities said.

Police said the gunman had 23 firearms in his hotel and an additional 19 at his home in Mesquite, Nev., about a hour northeast of Las Vegas. Authorities determined that more than 30 of the firearms were acquired in the past 12 months, an official said.

Neighbors describe him as surly, unfriendly and stand-offish. Mr. Paddock was the son of a bank robber who was once on the FBI’s Most Wanted list and who authorities described at the time as a “psychopath.” But Mr. Paddock’s brother said their father was not involved in their lives when they were children.

“He was always normal,” said Donald Judy, a former neighbor of Mr. Paddock’s in Mesquite, as he struggled to reconcile the friendly conversations about real estate and family and the carnage in Las Vegas.

Patrons and a bartender at Peggy Sue’s 50s Style Diner in Mesquite said Mr. Paddock and his girlfriend, Marilou Danley, would come in almost every week and have a few drinks and she would sing karaoke.

Ms. Danley, who lived with him, was born in the Philippines and is a citizen of Australia. She had been in Asia for at least two weeks before the shootings, her family denying she had any knowledge of his plans. Authorities said he transferred $100,000 to a bank in the Philippines days before the shooting.

Described by the police as a “person of interest” in the case, Ms. Danley was met by law enforcement officials after she arrived at Los Angeles International Airport from the Philippines late Tuesday night. She was being questioned Wednesday by federal authorities. Investigators are hoping Ms. Danley may hold the key to unraveling the mystery of what drove Mr. Paddock to carry out the massacre.

Victims of the tragedy are being remembered in vigils across the nation, including one planned for 6 p.m. Friday, Oct. 6, in Richmond. United Communities Against Crime is holding a candlelight prayer vigil outside the John Marshall Courts Building, 400 N. 9th St. in memory of the Las Vegas victims and the people affected by recent hurricanes, according to organizer Charles D. Willis. Participants are asked to bring candles.

President Trump and First Lady Melania Trump traveled to Las Vegas on Wednesday, visiting the hospital bedsides of the wounded and the base of police operations. He offered prayers and condolences for those who were killed and hurt, and praise and congratulations to first responders and doctors who rushed to save lives.

He also met with police officers, emergency dispatchers and others who had responded to the mass shooting Sunday night, telling them, “You showed the world and the world is watching, and you showed what professionalism is all about.”

The president, however, waved off questions about the availability of firearms — the shooter had a veritable arsenal of weapons — saying this is not the time to discuss the possibility of further gun restrictions.

Back in Washington, Republicans made clear on Wednesday they have no intention of taking up gun control measures, such as tightening restrictions on semiautomatic weapons and high-capacity magazines, in the shooting’s aftermath.

However, U.S. Sen. Dianne Feinstein, a Democrat from California, is launching another push to combat gun violence, this time targeting accessories that make it possible to convert a semiautomatic gun to fire rounds rapidly like an automatic weapon.

She said her bill, which had 26 Democratic co-sponsors as of Wednesday morning, would ban the sale, transfer, importation, manufacture or possession of bump fire stocks — also known simply as “bump stocks” — as well as trigger cranks and other accessories that accelerate a semiautomatic rifle’s rate of fire.

The longtime gun control advocate also revealed Wednesday that her daughter planned to attend the Route 91 Harvest Festival in Las Vegas, but didn’t go.