Las Vegas gunman Stephen Paddock has been described as a brilliant man who had an intimate knowledge of the second amendment and a room dedicated to his guns, according to a friend.

The Australian man, who wanted to remain anonymous, had multiple encounters with Paddock between 2013 and 2015 after he started dating his girlfriend's sister.

In an interview with the Guardian, the man said he knew Paddock to be highly intelligent and strategic but showed no behavior that could have predicted the massacre he carried out.

'He was extremely intelligent, methodical, conservative, guarded and strategic. A planning, thinking type of guy,' the man said, adding that Paddock won a a substantial amount of money using algorithms for gambling.

Scroll down for video

Stephen Paddock (seen left in DMV photo) and girlfriend Marilou Danley (right) lived in one of his properties in near Reno until August. Paddock killed 58 people in Las Vegas on Sunday

Photos of Las Vegas shooter, Stephen Paddock - seen in Manila (Philippines) in 2013 with relatives of his girlfriend, Marilou Danley; Marilou is believed to be in the purple top

He and his girlfriend, who was the sister of Marilou Danley, had also spent some time at their home Mesquite, Nevada where Paddock mentioned his 'gun room'.

'His comments were that it's a substantial hobby that needs to be protected: 'a gun room',' the man said.

As investigators reconstruct the life and recent activities of Paddock in a bid to work out a motive, details keep emerging that suggest the gunman's mental health had deteriorated on the months prior to the massacre.

Paddock had reportedly experienced significant weight loss in the lead up to the shooting. He also developed an obsession with his girlfriend's ex-husband, Geary Danley, with whom she had been married to for more than 20 years before they finalized their divorce in 2015.

The gunman's brother, Eric Paddock, told Reuters in a series of text messages that Danley was sympathetic in dealing with Paddock's allergy-driven quirks.

Paddock often wore brown cloth gardening gloves to prevent rashes from contact with cleaning chemical residues, the brother wrote.

He was also allergic to many pills and was unable to renew his pilot's license - he had flown planes since he was a teenager - because he could not take the pills needed to reduce his blood pressure. At casinos where he was a regular, he was such a valued customer that staff obliged his requests to wash his room's carpet with plain water.

'The reason Mary Lou looks so plain in that picture they keep posting of her is because for him she would not wear perfumes or hair sprays or anything with scents in it because it affected him,' Eric wrote, referring to the passport-style photo of Danley that has been widely circulated by news outlets.

Danley returned to the US on Tuesday after more than a week in the Philippines. Authorities have called her a 'person of interest' in the investigation and are hoping she can help crack the mystery of Paddock's motive.

The pair occupied this home in Verdi, but neighbors said they had barely any furniture and rarely opened their windows - and for some reason Paddock had a massive safe in his garage

On Monday this bomb squad arrived to check the home for booby traps ahead of a search by the FBI and ATF. A large black box was seized, as well as some of Paddock's 47 guns

But Paddock's brother said she might not be able to give investigators the clues they are hoping for because he fears he 'he manipulated around her'.

The portrait emerging of Paddock comes as more details are revealed of the arsenal of weapons he used to murder 58 people and injure 527 in Las Vegas on Sunday.

His weapon collection was worth tens of thousands of dollars and at least one was a made-to-order firearm made by Lewis Machine & Tool Company, a source told CBS.

Paddock had bought a total of 33 weapons between October last year and when he checked in the Mandalay Bay suit on September 28.

Neighbors who lived next door to Paddock and Danley when they were in Verdi, Reno had described him as an unfriendly, reclusive 'weirdo' who barely spoke and kept a sinister-looking giant safe in his garage.

The couple lived in the home up until August when they mysteriously packed up and vanished.

'I barely slept last night thinking about this evil man living next door with a house full of guns,' one neighbor, Susan Page, told The Sun. 'It could have been any of us he unleashed this horror on. It's just too much to even think about.'

Paddock, who made his money in real estate, bought the home, in the Del Webb Sierra Canyon retirement community, in 2012 shortly after it was built, according to public records.

But Page said that despite having the house for five years, the multimillionaire was practically a stranger to his neighborhood.

'They had barely any furniture in the house and nothing in the yard, the shades were always down and it was like they were not even living there,' she said.

A photo leaked Tuesday showed Paddock's body after he committed suicide in the hotel room he'd fired on civilians from. There also appears to be a letter on the table (in red circle), although police haven't announced finding a suicide note

Paddock fired on 22,000 people at a nearby music festival with 23 guns. Magazines can be seen stacked on the right. His Verdi neighbors are concerned that his safe held these guns

Others who lived next to a property he owned in Florida told CNN he would flit around from place to place, and admitted that he spent most of his time indoors playing online poker.

Paddock certainly seemed less open with his Reno neighbors; Page describes him as 'a reclusive weirdo' and says she 'never once got as much as a smile out of him.'

'I never heard music, conversation and never once saw them have friends over.

'He would keep his face down, avoid all conversation and was just very unfriendly and strange.'

Paddock (seen with Danley) was unfriendly, locals said. He never had music on or friends over, or engaged neighbors in conversation

Another neighbor, who did not want to be named, agreed, saying: 'Occasionally he would work out early in the morning at the community gym, but never ever does anyone here remember him having a friendly word to say to anyone.'

Unable to talk to him, his neighbors instead began to talk about him - and particularly about the safe in his garage.

'We would all wonder what on earth he kept in there, but nobody could ever ask as he was not the kind of man who engaged with anyone,' said the unidentified neighbor.

'It was as big as a refrigerator,' Page recalled. 'We would all joke and say, 'I wonder how much money he has stashed in there?'

'Now we are all horrified thinking maybe it wasn't money in there at all – but the guns he used to kill these poor people.'

It was also revealed that Paddock was prescribed anti-anxiety medication Valium back in June, which has been linked to increased aggressive behavior in multiple studies.

Paddock was taking 10 milligram tablets at the time of the massacre, though it is not known why he was prescribed them or whether he had underlying behavioral issues.

In total, police have found 47 guns across three locations - the house in Verdi, a second home in Mesquite, and the hotel room that Paddock used to fire on civilians.

The firearms were rifles, shotguns and handguns purchased in Nevada, Texas, Utah and California - all legally, over the course of more than 20 years.

Some 12 of the rifles found in the hotel room had been modified with legally available bump-stocks, which allow semi-automatic rifles to mimic full-auto guns, firing up to 800 rounds a minute.

Those weapons were found on Monday only after ATF, FBI and SWAT teams arrived at the home along with bomb disposal experts and robots to check for booby traps.

Mourners are seen here struggling to keep their emotions in check as they attend a vigil for the victims at the University of Nevada Las Vegas on Tuesday night

With the Mandalay Bay Resort and Casino in the background, a billboard advertising an upcoming gun show is seen along the Las Vegas Strip on Tuesday

Page's home was evacuated along with others on the street. When she was allowed to return home, she said, she saw something unusual.

'At some point after I was allowed to return home I saw them carrying a huge black box out of the house and loading it into the van,' she explained.

'It looked very much like an ammunition box to me.

'It is just terrifying to think what was going on next door to my home without any of us having any idea.'

Both Paddock and Danley disappeared from the home within a couple of weeks in August, Page said.

'I remember at the start of August looking out of my window and seeing Stephen pull up in a brand new huge silver minivan,' she explained.

'But just a few days later he left the house in it and was never seen again.'

She continued: 'I thought the whole situation was even weirder when two weeks later I then look out of my window again to see Marilou stuffing her car full of all her belongings.

'Over the course of three or four days it was like she was moving her entire life out of the house. She packed so much stuff not only was her car full, but it was also tied to the top of her car.

'After a few days of packing she too pulled out of the driveway and was never seen again.

'It was all very strange.'