American law enforcement say Stephen Paddock who shot at least 59 people dead in Las Vegas had amassed an arsenal of more than forty firearms.
While investigators are no closer to establishing what drove Vegas sniper Stephen Paddock to carry out his sick massacre, they have uncovered his alarming search history.
Authorities investigating the shooting that killed 58 concertgoers and injured more than 500 others have found internet search techniques used by local police for breaching rooms in standoff situations, a law-enforcement official reportedly told the Wall Street Journal.
The official reportedly said Paddock searched for information about how Las Vegas Metropolitan Police Department or SWAT teams force their way into rooms or buildings.
Investigators also discovered a laptop belonging to Paddock is missing its hard drive, making it more difficult to establish the motive in America's deadliest mass shooting.
The internet query and the missing hard drive are two more pieces of the puzzle authorities are yet to solve. However, ABC News reported Paddock is believed to have removed the hard drive before fatally shooting himself.
Investigators suspect gunman Stephen Paddock removed the hard drive from the laptop after opened fire from his high-rise suite at the Mandalay Bay hotel casino into a crowd at a country music concert, killing 58 people and wounded hundreds of others, an official said.
Investigators have been combing through every aspect of Paddock's life - from family, friends and associates to his travel patterns, health and finances.
The hard drive hasn't been found, according to the official, and the absence of digital clues adds yet another puzzling aspect to the investigation as authorities try to figure out what might've led the 64-year-old high-stakes gambler to commit the mass killing.
They even examined the gunman's brain to determine whether he was suffering from dementia.
Microscopic tissue examination can reveal otherwise hidden conditions such as dementia and chronic traumatic encephalopathy or CTE.
Paddock's brain has so far shown no obvious sign of tumour, injury or abnormality during a more routine autopsy conducted last week by Vegas coroners, according to officials - who have yet to release toxicology results or an official cause and manner of death.
BROTHER ARRESTED
Meanwhile, his brother, Bruce Paddock, has been arrested on suspicion of possessing child pornography.
Bruce Douglas Paddock, 59, was nabbed at an assisted living centre in North Hollywood, California on Wednesday morning local time.
A criminal complaint filed in Los Angeles County lists 20 potential counts and indicates the alleged crimes occurred in 2014, NBC News reports.
One of the counts is for possession of more than 600 images of children in porn, which includes 10 or more of a prepubescent minor, TMZ reports. Most of the counts involve sexual exploitation of a child.
ANOTHER TIMELINE
Digital investigators from the New York Times have formed their own timeline of the Vegas attack which places the shooting of Mandalay Bay security guard Jesus Campos about one minute into the attack - not before as authorities claim.
Staff working for the newspaper's video unit pieced together footage that was captured at the scene and apparently discovered that local police were wrong yet again about the order in which events occurred.
Instead of being shot right before the assault, they claim that Campos was targeted at 10.06pm - one minute after Stephen Paddock opened fire on the crowd at the Route 91 Harvest Festival.
"Ours isn't the definitive picture of what happened, more information will emerge, but it does give us new insights into what happened," senior story producer Malachy Browne told CBS News.
Flowers, candles and other items surround the famous Las Vegas sign at a makeshift memorial for victims of a mass shooting. Photo / AP
MASSACRE COSTS
On Wednesday, authorities also estimated that the costs of police, fire and other emergency services related to the massacre were projected at about US$4 million and climbing.
The disclosure came amid pledges by the federal government to provide US$1 million, and from the state of Nevada to pay US$600,000 to defray costs stemming from the October 1 shooting.
Las Vegas police Officer Laura Meltzer provided what she called a preliminary figure of US$3.5 million for department costs associated with the worst mass shooting in modern US history.
"We still have a lot of resources devoted to the investigation," Meltzer said.
"We still have people working overtime and around the clock on it." The amount spent on overtime to date amounts to more than half a percent of the annual Las Vegas police budget.
Clark County administrators on Tuesday estimated fire department, coroner and social services costs at between US$300,000 and US$500,000, county spokesman Erik Pappa said.
"Over the long term, we expect it will be in the millions," he said. Pappa noted that a facility dubbed the "The Vegas Strong Resiliency Center" opened Monday to serve as a one-stop resource for references and referrals for residents, visitors and responders affected by the shooting. He said it is expected to remain open for several years.
Paddock, a former real estate investor with homes in Reno and Mesquite, Nevada, fired assault-style weapons out two 32nd-floor windows at the Mandalay Bay resort into a crowd of 22,000 people at an open-air country music concert across the street. Police and the FBI have said they believe he acted alone. The U.S. Justice Department last week announced a $US1 million ($A1.2 million) award from "justice assistance" funds to Nevada to help defray immediate costs of responding to the shooting.
On Tuesday, Nevada Gov. Brian Sandoval and state Attorney General Adam Laxalt allocated $US600,000 ($A778,000) from funds that Laxalt said were reaped from a deceptive trade practices lawsuit settlement in July. Laxalt called the money non-taxpayer funds.
Sandoval called the money a first step in providing "any additional resources necessary" to help the investigation, and said the police department should receive the state money within 15 days.
The Las Vegas Metropolitan Police Department, with almost 2700 sworn officers, has an annual budget of US$552 million. It covers most of Clark County, with a population of about 2 million people and more than 40 million visitors a year. The annual county budget is about US$6.6 billion.
