Police are closing their investigation into the Las Vegas massacre - the deadliest mass shooting in modern US history - that took the lives of 58 people.

After 10 months of research and questioning, authorities announced Friday they are closing their books on the case after determining there was no evidence of conspiracy or a second gunman.

However police said they could not 'definitively' determine the motive behind lone-wolf shooter Stephen Craig Paddock's killing spree upon a Las Vegas music festival on October 1, 2017.

In a final report published Friday, it's revealed that Paddock had spent a whopping $1.5million in his last two years, claimed he was sick, and his own brothers believed he was 'paranoid and delusional'.

Officials announced Friday they will close the investigation into the Las Vegas massacre, the deadliest mass shooting in modern history, a person pictured on ground in aftermath of the October 2017 shooting

The horrific shooting was determined to be led by 64-year-old Stephen Craig Paddock alone where he opened fire on an outdoor country music concert in Las Vegas, aftermath above

The 10-month investigation determined there was no evidence of conspiracy or a second gunman, but failed to find a motive behind his deadly massacre

Clark County Sheriff Joe Lombardo said Paddock was 'an unremarkable man' who showed signs of a troubled mind leading up the attack on the busy strip.

'What we have been able to answer are the questions of who, what, when, where and how,' Lombardo said upon the release of a 187-page police report.

'Without a manifesto or even a note to answer questions the totality of the information that has been gathered leaves us to only make an educated guess as to the motives of Stephen Paddock,' he added.

With the closure of the 10-month investigation by the Las Vegas Metropolitan Police Department, no one else will be charged in connection with the shooting as it's determined that Paddock acted alone.

The 10-month investigation determined gunman Steven Paddock, 64, acted alone

Officials added the attack had no link to international terrorism, despite claims by The Islamic State group that they were responsible for the attack.

Paddock, of Nevada, released a hail of bullets from the 32nd floor of the Mandalay Bay Resort casino and hotel around 10pm that night, firing onto a country concert crowd of 22,000 people below.

The final investigation report revealed that Paddock believed he was sick, repeatedly complaining to his girlfriend that he was ill and doctors could not cure him.

His girlfriend Marilou Danley, 62, said his doctors diagnosed him with a 'chemical imbalance'. She added he'd get 'very bad headaches' from chemical smells, would often need to change hotel rooms, would not shake hands with people, and often wore cotton gloves.

Marilou added that Paddock, a self-described atheist, would tell his Catholic girlfriend 'Your God doesn't love me'.

Paddock's doctor told cops he didn't have any major ailments but 'may have had bipolar disorder' for which he refused treatment including antidepressants. But he accepted prescriptions for anxiety medication.

His doctor also described his behavior as 'odd', showed 'little emotion' and 'seemed fearful of medications'.

His brother Bruce Paddock, although they hadn't spoken for more than 10 years, said the gunman was 'delusional'.

Clark County Sheriff Joe Lombardo announced the 10-month investigation into the massacre was closing on Friday August 3 without finding a motive behind the terrorizing attack

Paddock opened fire onto the concert crowd below from the 32nd floor room of the Mandalay Bay Hotel on the Las Vegas strip, room pictured above

A view inside his room at the Mandalay Bay Hotel were he launched his attack reveals his firearms strewn on the beds and the shattered window from where he opened fire

A closer look at the broken window reveals his line of sight on the 32nd floor, from where he launched his violent attack

Bruce believed his brother suffered from 'mental illness and was paranoid and delusional', the report made public Friday said.

He added that he did not believe his brother was a 'violent person' or abused drugs or alcohol.

That Friday report also revealed that Paddock had spent a shocking $1.5million over the past two years. Much of that money was paid to casinos.

The report included a summary of 14 of Paddock's bank accounts.

In September 2015 Paddock had $2.1million in the accounts. Two years later in September 2017, a month before his shooting, the amount dropped to $530,000.

Sheriff Lombardo said Paddock was a reclusive, high-stakes gambler but he wasn't 'as successful in the gambling as he was in the previous years'.

He paid $600,000 to casinos and more than $170,000 to credit card companies.

As for his heavily armed attack - he spent nearly $95,000 in firearm related purchases.

His brother Eric suspects him of cheating on tax preparations.

Earlier this year, federal prosecutors brought criminal charges against a man named Douglas Haig who they say sold 720 rounds of armor-piercing bullets to Paddock. He has pleaded not guilty.

Footage from police body cameras was released on Wednesday July 25, revealing the chaos and panic that followed the shooting at the outdoor country concert on October 1, 2017

Police body cam footage reveals an officer pointing his gun in search of what authorities though at the time were multiple shooters inside and outside a Las Vegas strip hotel

Another police body cam shot reveals armed forces at the scene searching for the shooter

Police pictured directing Las Vegas concert goers to safety after following the hail of bullets

Police stand at the scene of the mass shooting near the Mandalay Bay hotel, where Paddock fired from his room on the 32nd floor onto concert goers below

Police have released 13 batches of investigative documents, 911 audio, police reports, witness statements and video over the last three months.

They have illustrated chaos, heartbreak and heroism from police, first-responders, concert-goers and more.

Body camera recordings made public earlier this year displayed officers using explosives to blast through the door of a 32nd floor hotel suite to find Paddock dead on the floor from a self-inflicted gunshot.

Several assault-style weapons fitted with rapid-fire 'bump stock' devices were strewn about the suite.

Police said that he was surrounded by 24 guns including 10 AR-15 semi automatic rifles, most of them with 100-round magazines in the hotel.

An additional 18 guns were recovered at his home in Mesquite, Nevada and another seven in his Reno, Nevada home.

Also recovered in his hotel room was a laptop but the hard drive on the machine was missing. However, child pornography was found on that laptop.

A psychological profile on Paddock will be released later this year by the FBI's Behavioral Analysis Unit.

The report says many described him as a narcissist who 'only cared about himself'.

His brother Eric told investigators he believed Paddock carried out the attack 'because he had done everything in the world he wanted to do and was bored with everything.'

He said his brother 'would have planned the attack to kill a large amount of people because he would want to be known as having the largest casualty count', according to the report.