At 10:05 PM on Sunday in Las Vegas, country music star Jason Aldean was delivering the closing set at the Route 91 Harvest music festival when gunfire rang out. At first attendees and performers confused the sound as part of the show’s pyrotechnics, until quickly realizing bullets were flying.

For 10 minutes on October 1, a lone gunman checked into the luxury Mandalay Bay Resort and Casino, utilized his 32nd floor suite as a perch to rain fire down upon concertgoers at this country music event being held across the street, committing the deadliest mass shooting in U.S. history.

Stephen Paddock, 64, a retired accountant with no criminal record, fired more than 1,100 rounds into the crowd of 22,000, killing 58 people and injuring 546. Many victims were struck in the head and back, with incidental injuries coming as automatic gunfire ricocheted off concrete until finding flesh. This incident surpassed the 2016 Orlando nightclub shooting, where 49 died (excluding the gunman).

Paddock scouted other outdoor festivals, but checked into Mandalay Bay on Sept. 25, where management gave him a complimentary room as a perk for being a frequent high-stakes gambler. After a three night stay he moved to the 32nd floor suite. Here Paddock stockpiled an arsenal of weapons.

In more than 10 suitcases, Paddock brought 23 firearms to his suite, a large quantity of ammunition and numerous high-capacity magazines capable of holding up to 100 rounds apiece. Twelve of the weapons were fitted with bump stocks, used to convert semi-automatic weapons into auto-fire, and two rifles were equipped with telescopic sights.

Hotel security responded to an open-door alert on the 32nd floor minutes before the shooting began. After hearing a drilling sound, Security Officer Jesus Campos approached Paddock’s suite and was shot in the thigh by one of the 200 bullets fired through the door. Later it was discovered Paddock had installed cameras inside and outside his hotel room to monitor hallway activity.

Police were initially confused where the shots were coming from before spotting multiple muzzle flashes in the tower at Mandalay Bay. Officers reached the 32nd floor at 10:17 PM, and encountered the wounded Campos. With the shooting stopped, police worked for the next hour to evacuate hotel guests.

At 11:20 PM, Room 32135 was breached by police with explosives, where inside Stephen Paddock was found dead on the floor from a self-inflicted gunshot wound. A note found in the room showed Paddock had calculated the distance, wind and trajectory from his 32nd floor hotel room to the concertgoers located 490 yards away.

What sets this attack off from others, in addition to the stagger number of dead, is the perpetrator. He doesn’t fit the usual demographics of a mass murderer. There’s nothing about his persona that would explain his committing this hateful act.

Paddock was considerably older than most who commit these crimes. He was twice divorced with no children, and described as a retired former auditor and real estate businessman, with no military background, political or religious affiliations, who resided comfortably in a retirement community in Mesquite, NV, 82 miles from the Las Vegas shooting scene. Yet another cache of weapons was discovered at his home.

It’s believed his net worth exceeded $2 million, and he was regularly seen for 25-years in high-limit gambling rooms around Las Vegas. Video poker was his game of choice, a solitary endeavor, that he enjoyed playing well into the early morning hours – choosing instead to sleep during the day.

He appeared on the surface as a rather mundane individual aside from one odd background fact. Paddock was the son of Benjamin Paddock, a bank robber who was on the FBI’s most-wanted list between 1969 and 1977.

The most confounding aspect to this crime is that after following thousands of leads police have been unable to establish a motive for why Paddock committed such an atrocity. It’s pure evil just to conceive such an act, but this took time. It required planning, a target had to be identified and scouted, weapons and ammo needed to be amassed, and then actually pulling the trigger. What happened to this man?

Law enforcement is scrambling to find an answer. They can deal with a plethora of horrible actors if the “why” is understood. Paddock scares the hell out of them because he gave no overt signals something was troubling him, and his purchase of weapons was legal. This type of crime will be very difficult to prevent in the future – especially if one is willing to die in carrying it out.