We don't know why Stephen Paddock opened rapid fire on a crowd of thousands, killing 59 and wounding more than 500.

"We are completely dumbfounded,” his brother Eric Paddock told reporters. “We can't understand what happened."

Las Vegas Assistant Sheriff Todd Fasulo pleaded for patience during the investigation, saying authorities were "hunting down" every clue to learn more.

President Trump explained it this way:

"He was a sick man, a demented man with a lot of problems, I guess, and we are looking into him very, very seriously. We are dealing with a very, very sick individual."

Google searches for Stephen Paddock motive have reached a fever pitch. But what are searchers hoping to find?

Why do we clamor to make sense of the senseless?

Trying to understand such a massive tragedy is "a natural reaction," said psychologist Seth J. Gillihan, who researched Post-Traumatic Stress Disorder at the University of Pennsylvania. And there are many emotions and thought processes in play.

Political Schadenfreude

"There's an urge to hope to identify the shooter with the political party that one is opposed to — hoping the shooter is a liberal or a conservative — and some would take comfort or even joy in that fact, and I don't think we should do either," Gillihan said. "In neither case would this person be representative of those groups."

People demonstrated this urge almost from the moment the tragedy unfolded. Several websites falsely stated that the gunman was anti-Trump and pro-Obama, Rachel Maddow and MoveOn.org, according to PolitiFact. Antifa was (wrongly) blamed. ISIS claimed responsibility, but law enforcement said there was no merit to that. A conservative commentator incorrectly claimed it was a Muslim terrorist attack. And that's nothing to the individuals flooding social media.

Sense of control

Another reason to seek motive is the same reason motive is sought for any crime — the desire to prevent it in the future. Understanding the cause of the threat "makes us feel a little safer," Gillihan said. For example, if there is a murder near your home you would feel fear — but if you find out it was the victim's brother-in-law instead of a random crime, the "it could've been me" feeling dissipates, he said.

"There's a real sense of loss of control when something like this happens. We think, 'my God, I've been to a concert ... this could happen anywhere, anytime' and we want to make sense of a senseless situation," Gillihan said. "Our minds don't rest easily not knowing the cause of something so baffling and monstrous and shocking. We'd like to be able to organize that experience, to put a box around it, with arrows to say, 'OK, x led to y.'"

'I just want closure'

Herman Gold escaped the hail of bullets in Las Vegas, but returned to the site of the concert the next day.

“I just want closure,’’ Gold said. “Why? What’s the reason that on that particular night, one individual would sacrifice everyone else for his insanity?’’

Having an answer to those questions may help survivors move on.

"To know what was going through this person's head to lead them to do something so —not just murderous but intentionally big that it required planning and preparation — that a person could go through all of that it does leave this big question mark," Gillihan said. "So it could complicate survivors' sense of trust. 'How do I trust other people when human beings are capable of doing something with no known motive?'"

What if we never get a reason?

Paddock is dead and the possibility of never understanding his motive would "leave open this parenthesis that never closes," Gillihan said.

There are many reasons to try to close it, not the least of which this one:

"Even if we never know for sure what [the motive] is, it's worth going through some of that together — it's a shared activity we engage in as a broader community trying to make sense of something we're all troubled by. So it may in the end not be fruitful, but I wouldn't say it's futile."

Contributing: Josh Peter and John Bacon, USA TODAY