Police are still trying to determine what motivated Stephen Paddock to rain gunfire on some 22,000 music fans along the Las Vegas Strip Sunday night. The attack left 59 people dead and 527 people were injured, in the worst mass shooting in recent U.S. history.

Paddock unleashed a prolonged and vicious assault from the 32nd floor of the Mandalay Bay Resort and Casino shortly after 10 p.m. local time, as musician Jason Aldean was performing. Aldean had been scheduled to go on at 9:40 p.m., as the last act of the three-day festival.

Responding to what he called rumors of multiple attackers at the concert, Assistant Sheriff Todd Fasulo has said that officials “have no information or evidence” that there was anyone but a solo gunman responsible.

Here’s more of what we know about crucial elements of the case:

The guns

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Responding to calls that a concert venue was under assault, police officers almost immediately reported that they were facing fully automatic gunfire.

Police say they found 23 firearms in the Mandalay Bay hotel room where Stephen Paddock fired down on the crowd and 19 in his home in Mesquite, Nev. The guns at the hotel included fully automatic weapons, according to California Rep. Adam Schiff, of the House Intelligence Committee, citing a briefing from FBI officials.

“In other mass shootings — at Newtown; San Bernardino; Aurora — killers use those semi-automatic weapons,” NPR’s Joseph Shapiro reports on Morning Edition. “They reload automatically, but they shoot just one round for every trigger pull. And those fully automatic weapons are very hard to come by. They’re highly regulated. And as a result, they’re rare rarely used in crime. So this would add an even more gruesome detail.”

Some rifles had also been modified to be virtually fully automatic. The Associated Press says investigators found two “bump stock” devices — simple modifications to the gun’s shoulder stock that often cost around $300 — though that detail hasn’t been officially confirmed. The devices convert energy from guns’ natural recoil to fire much faster than a normal semi-automatic weapon.

As for legal fully automatic weapons, Joseph says:

“If they were made before 1986, you can still get one legally. You have to pay the tax, it’s still $200. You get a background check, you register your fingerprints with the Bureau of Alcohol Tobacco and Firearms. But there aren’t a lot of those legal ones around. In 2006, there were fewer than 400,000 on the machine gun registry. So they’re hard to find, and that means they cost a lot — about the price of a small car.”

At least one gun store near Paddock’s home has released a statement saying he passed background checks and that all legal procedures were followed. Other stores and gun ranges in the area have also acknowledged being in contact with authorities about Paddock, according to NBC News.

The ATF is tracing the weapons’ histories, as well as breaking them down to determine which ones were used in the attack — and which ones might have been further modified, Clark County Sheriff Joe Lombardo said.

Remembering the victims

Charleston Hartfield, an off-duty police officer, was among those killed; so was special education teacher Sandy Casey, who was at the concert with her fiancé. Navy veteran Christopher Roybal of California also died — after surviving gun battles in Afghanistan.

All the names of the dead and injured have not yet been released, as police and investigators process the scene and inform families and loved ones.

Among those killed were Sonny Melton, a registered nurse from Big Sandy, Tenn. — his wife says he saved her life at the concert.

Heather Melton told USA Today, “He grabbed me from behind and started running when I felt him get shot in the back.”

Sandy Casey worked at Manhattan Beach Middle School in Los Angeles County, where an official said Monday she was “absolutely loved by students and colleagues alike and will be remembered for her sense of humor, her passion for her work, her devotion to her students, her commitment to continue her own learning and taking on whatever new projects came her way,” according to member station KPCC.

Rachael Parker, a records technician in the Manhattan Beach police department, also died in the attack — she was one of four department employees who were at the festival. One of her colleagues was also shot, suffering minor injuries.

We have a separate story about those who lost their lives in the Las Vegas attack; we’ll be adding to it as their names and stories emerge.

The public response

A GoFundMe campaign for victims of the shooting and their families has raised some $3.5 million since it was started on Monday by Clark County Commission Chair Steve Sisolak.

After city officials made repeated calls for blood donations on Monday, Las Vegas Assistant Sheriff Todd Fasulo said, “They have enough supply to last them for the foreseeable future.”

Even before those calls went out, residents and visitors had been lining up to donate — prompting still more volunteers to show up with water and snacks for those waiting.

As of Tuesday, local officials were asking people to contribute to charities, saying they’ve been overwhelmed by support.

“Shows of support have been amazing & greatly appreciated,” Clark County said via Twitter. “First responders have enough items to deal with immediate need.”

On Monday evening, the Las Vegas City Hall hosted a prayer vigil to honor those who lost their lives in the violence. As images from the scene show, many people bowed their heads in silence and listened to religious and city leaders. And as the event ended, music and singing broke out.

An incredibly diverse group of people keep the prayers going long after many have left. Las Vegas City Hall vigil pic.twitter.com/NtNSNQ6O7H

— Janna Karel (@jannainprogress) October 3, 2017

After darkness fell, the exterior of City Hall was lit up with the colors of the American flag.

Las Vegas City Hall lit up like a American flag tonight. @CBSLA pic.twitter.com/HH6Sdp9MQq

— Tina Patel (@tina_patel) October 3, 2017

The attacker

The gunman, identified as Stephen Craig Paddock, 64, lived in a retirement community in Mesquite, Nev. He was twice divorced and reportedly loved to gamble at Las Vegas casinos, as NPR’s Scott Neuman reported.

Police have said they haven’t found a manifesto or other type of direct explanation for why Paddock would have carried out such a violent act.

So far, a motive in the case has been elusive, says NPR’s law enforcement correspondent, Martin Kaste.

“This man is not fitting any of the common profiles we’ve come to expect for perpetrators of these mass shootings,” Martin reports. “He’s an older man. He apparently had enough money — apparently well to do, actually, from real estate investments. He didn’t have any known sort of religious affiliation that might have driven him to this. There was no sort of cause that he’d espoused that anyone knew about.”

Investigators are going through a computer and other electronic devices they recovered, hoping to find out more about Paddock and the possible reasons for his actions.

Police say they believe Paddock killed himself. A SWAT team used an explosive to breach Paddock’s room, and Sheriff Lombardo said that when police entered, they “found the suspect dead.”

Key sites investigated

Officers who approached Paddock in the hotel room and who visited his properties have been wary of booby traps, Lombardo said.

Giving a rough estimate of the distance from Pollard’s hotel room to the concert venue, Sheriff Lombardo said he believes it to be “in excess of 500 yards.”

He added that police have been focusing on four different locations:

• The concert venue at Las Vegas Village, an outdoor space across from the Luxor Hotel and Casino and northeast of the Mandalay Bay Resort and Casino;
• Room 32135 at the Mandalay Bay Resort and Casino, from which Paddock carried out the attack after checking into the hotel on Thurs., Sept. 28. His
• A house in northern Nevada that was breached by a SWAT team on Monday;
• Paddock’s residence in the Sun City retirement community in Mesquite. Monday’s search of that property turned up explosives, along with thousands of rounds of ammunition.

In addition, law enforcement officials found “several pounds” of ammonium nitrate fertilizer — which has been used in attacks utilizing explosives in the past — in Paddock’s car.

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