Did mass killer have a brain disorder?
Was Stephen Paddock, as some have suggested, simply a 'psycho' who had no motives for killing 59 people in the Las Vegas massacre?
David Eagleman, a professor of neuroscience at Stanford University, told CNN: "A person might be psychotic (e.g. with schizophrenia, which is a disorder of cognition), or they may be psychopathic (someone who doesn't care about others). Either could be considered here."
Paddock was almost certainly not schizophrenic, says the professor.
"As far as we can tell he had no history of schizophrenia, and besides that, he was 64 years old. Schizophrenia is a young person's disorder, usually surfacing during the late teens or early twenties.
"Could he have been a psychopath (also known as a sociopath)? Possibly. His father, Benjamin Hoskins Paddock, a bank robber, is claimed to have been a psychopath (I have no real evidence of that diagnosis beyond the news reports). Psychopathy is heritable, at least in part, as revealed by analysis of identical twins -- however, keep in mind that most mental issues are a combination of nature and nurture.
"The fact that Paddock was divorced twice is certainly consonant with psychopathy; strings of broken relationships are typical among psychopaths. However, the rest of the data about him is too thin to insist on psychopathy."
In fact, people who knew Paddock - his brother and his neighbours - seemed shocked by what happened. His brother claimed that Paddock recently sent a walker and boxes of cookies to their mother - not typical of psychopathic behaviour.
His girlfriend, also describes him as "kind and caring". However, a family friend of Paddock has revealed details of the strained relationship between him and his girlfriend - as well as his liking of casino-sponsored prostitutes.
Australian businessman Adam Le Fevre was in a relationship with the sister of Marilou Danley – the partner of Las Vegas gunman Stephen Paddock.
Mr Le Fevre told A Current Affair he went to Las Vegas with Paddock, 64, two years ago with his partner Liza and her sister Marilou, and had travelled to the Philippines with him twice, first in 2013.
He said Paddock was 'condescending' towards Ms Danley, 62, making her 'nervous and jittery', while also making the most of prostitutes offered to him by casinos.
Professor Eagleman wonders if Paddock was suffering with a brain tumour which caused his uncharacteristic behaviour.
"Is it possible that there were changes in Paddock's brain, such as a growing tumor? This is always a question that needs to be considered, especially as there was apparently little about Paddock that foreshadowed this monstrous act. Las Vegas police said they had not previously even known his name.
"There's absolutely no way I could conceive that my brother would shoot a bunch of people that he didn't know," his brother Eric said. "Something just incredibly wrong happened to my brother."
Strokes or a traumatic brain injury can cause changes in behaviour. And one disorder in particular deserves mention: frontotemporal lobar degeneration (FTLD). It refers to a deterioration of two lobes of the brain, the frontal and the temporal: two regions that underpin much of the decision-making and emotion that makes us social creatures.
As these brain areas degrade, people develop frontotemporal dementia (FTD) - and this often comes hand-in-hand with violent, asocial behaviour.
"When I heard Paddock's age, I immediately began to wonder about this, as the onset of the disease is typically in a person's late 50s."
Question is: Will we ever know the truth?