On Monday, a 64-year-old Nevada man named Stephen Paddock booked a room at the Mandalay Bay hotel and casino in Las Vegas on the 32nd floor, took 23 guns out there with him, and opened fire from his window on the country music festival that was taking place across the street. He killed 59 people and injured 527 more before shooting and killing himself as the police arrived on the scene. It was the worst mass shooting in American history.

An investigation is now underway by local authorities in Las Vegas, and new details are coming to light. For starters, the gunman had a 62-year-old Australian girlfriend and roommate named Marilou Danley who was in the Philippines at the time of the shooting.

She has been named a "Person Of Interest" in the case and has just returned to the US to answer the police's questions. Being in the Philippines was either a coincidence (or Paddock simply waited for her to leave before carrying out his big plan) or a way of establishing an alibi in order to avoid being connected to the case. That's what the police are hoping to find out when they question her today.

Clark County's Sheriff Joseph Lombardo confirmed at a press conference that the investigators have been in touch with Danley in the wake of the attack. The Sheriff said that communication and questioning with Danley is "ongoing" and added that the investigators are expecting "some further information from her shortly" about the Vegas shooting.

He confirmed that she is still a "person of interest," having previously been cleared of any connection to the attack, as it was discovered that Paddock had wired $100,000 into a bank account in the Philippines about one week before the shooting. Sheriff Lombardo declined to comment on this.

Paddock's detailed planning revealed by police

The investigation has also turned up the meticulous planning that Paddock did in anticipation of the shooting. He had everything about the Las Vegas massacre planned down to the last detail, which makes the fact that his motive remains unknown even more confusing. For one, it was discovered that Paddock had set cameras up in his room, as well as two out in the hallway and one in the peephole, to capture the action.

Lombardo attributes the placement of cameras to a desire to go down in history for his crimes, a la Jigsaw or John Doe from the movie "Seven." He believe that Paddock set up the camera so that he would see "anybody coming to take him into custody." Police body cam footage of the Las Vegas attack has also been released. Paddock was apparently firing his weapons for "somewhere between nine and eleven," until the police showed up to stop him. US President Donald Trump has described the police department's response time as "incredible."

Lombardo said that the most "troubling" information that has come from the investigation into the Las Vegas massacre is that they've deduced that Paddock "evaluated everything" that he did on Monday night.

He said that, with regards to this mysterious unknown motive of his, they believe that he may have been "radicalised," and so they're searching for the "source" of that radicalisation.

ATF declares all of Paddock's 47 firearms legal

The grand total of firearms found at various locations where Paddock was before he committed the attack and then killed himself, including two of his properties and the Vegas hotel room where he did it, has now been confirmed as 47 by the Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF). ATF Agent Jill Snyder has declared all of Paddock's weapons legal, having been purchased in California, Nevada, Texas, and Utah. So, he planned this deadly shooting completely within the confines of the law. That's safe, right?