Not long after the final blast from the muzzle of Stephen Paddock's rifle cut through the Las Vegas night, the search for his motive began.
Five days later, authorities are still searching.
Paddock killed 58 people and injured almost 500 more, then killed himself. But he seems to have been, as his brother described him, "just a guy".
Instead of filling a void, the search has simply shown how deep the hole is. And the deeper the hole, the louder the echo.
This is good news for Islamic State, who claimed without evidence in the hours after the attack that Paddock was a "soldier of the caliphate".
If, only a few hours later, police had found a manifesto by Paddock raging against casinos or Vegas or country music, and it had nothing to do with Islam, the IS propaganda machine would have taken a significant hit.
But there is no manifesto. There's nothing that shows Paddock was motivated by Islamic State; but nothing that shows he wasn't, either.
There is no evidence, in fact, that the slaughter was motivated by anything at all.
Paddock was a professional gambler who lived in a housing complex for those aged over 55. But, according to IS boasts in the hours after the attack, he converted to Islam "a few months ago" and was bestowed the Arabic name Abu Abd El Bar.
In the following days, IS clarified further: Paddock converted six months ago, and was known as Abu Abdul Barr al-Amriki, they claimed.
There has been no clarifying evidence provided from the terror group, Paddock's family or friends, or authorities, including the FBI and CIA.
"He has no political affiliation, no religious affiliation, as far as we know," brother Eric Paddock said. "This wasn't a terror attack."
Paddock's partner, Marilou Danley, was in her native Philippines at the time of the attack.
By the time she travelled back to the US, she was seen as the key to the case: if the answers had not been found in the hours immediately afterwards, the truth must lie with her, was the logic. Eric Paddock had described her as the closest person to his brother.
But she did not know why either.
"He never said anything to me or took any action that I was aware of, that I understood in any way to be a warning that something horrible like this was going to happen," she said.
FBI special agent Aaron Rouse confirmed the day after the attack that the bureau had "determined to this point no connection of an international terrorist group".
But there were others in authority who were less definitive.
"This person may have been radicalised, unbeknownst to us, and we want to identify that source," Las Vegas Metropolitan Police Department Sheriff Joe Lombardo said in the hours after the attack.
He bordered on speculative in the following days, when he said he was not convinced Paddock had acted alone, and questioned whether he had deliberately concealed the motive.
There was a note in Paddock's hotel room, he added. But it was not a suicide note, and it seemed not to have illuminated or explained anything about a motive.
"What we know is, Stephen Paddock is a man who spent decades acquiring ammunition and weapons and living a secret life, much of which will we'll never fully understand," Lombardo said.
All this means it may never be known why Paddock committed the worst mass shooting in recent US history.
So why would IS, the biggest brand name in global terror, claim him as one of their own?
Under "normal" circumstances, the terror group claims an attack if they helped actively plan it; if they sent the offender; or if the offender drew inspiration from IS.
At 64, Paddock would have been the oldest IS recruit from the US by nine years, according to George Washington University research.
He had no known online profile or social media accounts, meaning there is no evidence that he had gravitated towards radicalism.
Nothing was found on his electronic devices that indicated he had self-radicalised or was in communication with IS.
He was, therefore, not in obvious contact with IS, nor a sympathiser, and did not fit the demographic profile of a radical.
Which leaves the circumstances of the attack.
If anything, recent IS messaging has emphasised the ease of mounting unsophisticated strikes using trucks or vans, and knives rather than guns.
Paddock's attack certainly did not lack sophistication: hidden cameras to monitor movement outside his room, evidence he had scoped other locations, and then the troubling potency of his arsenal: 47 guns, 33 that he bought in the past year, bump stocks which allowed some of them to fire automatically, 1600 rounds of ammunition and 22 kilograms of ammonium nitrate.
It was an armoury any terrorist group would be proud of. But Paddock seemingly bought all of it legally, with his own money.
All of this appears to add weight to the suggestion that IS claims about the Las Vegas massacre are false; the third recent occasion of the terror group incorrectly taking credit for an attack.
Last month, it claimed responsibility for a bomb plot at Charles de Gaulle airport in Paris, and in June it said that a man who killed 36 people at a Manila casino was one of their "fighters".
Both statements were released by its Amaq news agency, which also hailed Paddock this week. Both were found to be false within days. The Manila attacker was a problem gambler, and the airport evacuation was not caused by a bomb threat.
But while IS has a shaky recent track record, it is a misconception that the group has a record of incorrectly claiming attacks. (An article published in the UK this week entitled "Isis just claimed responsibility for Theresa May's cough" sums up the sentiment.)
Rukmini Callimachi, who covers IS for the New York Times, tweeted that in her rough analysis of more than 50 cases the group had claimed, only three were false.
There were also attacks which they could have claimed - because IS flags were found at the scene, or because of the background of the offenders - but did not.
The main thrust of her argument was that the group is right more often than wrong.
She also dismissed the suggestion that claiming credit for the attack was a sign the group was struggling for legitimacy as coalition forces take hold of its territory in the Middle-East.
Experts have argued that the IS propaganda machine is no longer slick and disciplined, and is over reaching to claim violence against "crusaders".
"It seems like they're desperate for attention and will claim just about everything," Rand Corporation terrorism expert Colin Clarke told CNBC. "They've lost so much territory, and they fear they're becoming irrelevant."
But other experts believe the IS propaganda machine is stronger than ever.
In a study published in the Australian Journal of International Affairs before the Las Vegas attack, Macquarie University counter-terrorism expert Dr Julian Droogan writes that IS had found new ways to communicate, despite being pushed from Facebook, Twitter and YouTube, especially through their Rumiyah magazine, which is translated into several languages.
"The Islamic state-building prospect is going to fail but when it does it will not be the end of the ideas," he said.
Regardless of whether there was IS involvement, was the Las Vegas shooting terrorism? Some angry commentary in the aftermath of the shooting claims that Paddock was a terrorist because he caused terror, and the only reason he was not being accused of that crime was because he was white, and not Muslim.
Under Nevada law, in fact, his mass shooting would be considered an act of terrorism. The State Statute defines terrorism as anything that involves the use of violence to cause death to the general population.
Under American Federal law, another element is required - political motivation. Terrorism is defined as using "violence against persons...to intimidate or coerce a government, the civilian population, or any segment thereof, in furtherance of political or social objectives".
The question of criminal liability is, of course, a moot point: Paddock is dead, so will not be charged, regardless of where his crimes were committed.
Which leaves the simmering political argument about whether acts of mass violence committed domestically in the US - typically by white men with opaque motivations - should be considered terrorism. And if so, what is their defining "political or social objective".
As White House press secretary Sarah Huckabee Sanders offered, when asked if the Las Vegas shooting was an act of domestic terrorism: "It would be premature to weigh in on something like that before we have any more facts".
