Stephen Paddock, who killed 58 people and wounded more than 700 others in a mass shooting in Las Vegas in October of 2017, carefully planned his attack for months, according to a new report published by the Las Vegas Police Department.

In a new preliminary report published on Thursday (Jan. 18), investigators meticulously piece together a timeline of events leading up to the shooting, which began during Jason Aldean's set on the third and final night of the 2017 Route 91 Harvest Festival. Using interviews, forensic evidence, eyewitness accounts and a search of the gunman's hotel room and computer, authorities paint a disturbing picture of an increasingly isolated man who planned every aspect of his crime well in advance.

Paddock's girlfriend, Marilou Danley, tells investigators that Paddock had grown more and more distant in the months before the attack and that she knew he had bought a large number of guns, which she believed was just a hobby. When they stayed together in September of 2017 at Mandalay Bay — where Paddock would later conduct his attack by firing into the crowd from his hotel room — "she observed Paddock constantly looking out the windows of the room which overlooked the Las Vegas Village venue. Paddock would move from window to window looking at the site from different angles," according to the report.

A doctor who had treated Paddock called him "odd" and said he showed little emotion. That doctor felt Paddock might be struggling with bipolar disorder, which Paddock refused to discuss, though he did accept medication for anxiety.

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Police found "several hundred images" of child pornography on the four laptops recovered from Paddock's room, and his "disturbing" search history indicated that he had been looking for the perfect location to conduct his rampage for at least several months. His searches included "summer concerts 2017," "biggest open-air concert venues in USA," "how crowded does Santa Monica Beach get," "How tall is Mandalay Bay," "life is beautiful expected attendance" and "do police use explosives," among other phrases.

Investigators also found dozens of guns in Paddock's room, and confirmed that in the year prior to the shooting he had legally purchased 55 firearms. They also found several handwritten notes, including one with written measurements and distance and bullet drop calculations.

According to the preliminary report, Paddock used several large suitcases to smuggle his guns into the hotel over a period of days to avoid suspicion, and police also recovered several surveillance cameras that he used as a makeshift alert system in the hallway outside his room to let him know when authorities were approaching. He was dead from a self-inflicted gunshot wound to the head when police broke his door down after his shooting spree, and despite the investigation, investigators have established no motive for the crime.

The Las Vegas Police Department are still involved in an ongoing investigation, with a more thorough final report still expected, possibly by the end of 2018.

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