Criminal investigation

Investigators reportedly believe Las Vegas gunman had undiagnosed mental illness

It is unusual to have so few hints of a motive five days after a mass shooting. In previous mass killings or terrorist attacks, killers left notes, social media postings and information on a computer — or even phoned police.

"The lack of a social media footprint is likely intentional," Erroll Southers, director of homegrown violent extremism studies at the University of Southern California, told the Associated Press "We're so used to, in the first 24 to 48 hours, being able to review social media posts. If they don't leave us a note behind or a manifesto behind, and we're not seeing that, that's what's making this longer."

What officers have found is that Paddock planned his attack meticulously.

He requested an upper-floor room overlooking the festival, stockpiled 23 guns, a dozen of them modified to fire continuously like an automatic weapon, and set up cameras inside and outside his room to watch for approaching officers.