(CNN) Authorities on Friday released a preliminary investigative report on the Las Vegas shooting in response to large public interest in the case.

Many questions -- such as the motive -- remain unanswered since the October 1 massacre in which 58 were killed and hundreds injured when the gunman, Stephen Paddock, opened fire on the Route 91 Harvest music festival from the 32nd floor of the Mandalay Bay Resort and Casino.

Clark County Sheriff Joe Lombardo said the FBI is investigating an individual of federal interest related to the case. Charges could be brought within 60 days, he said.

Here is what we have learned from the report.

New information about the investigation

A window broken by Paddock and the interior of his hotel room.

• Authorities have determined how many victims were injured. Officials told reporters Friday that investigators determined 422 people suffered injuries as a direct result of gunfire, while another 851 individuals suffered other injuries during the attack. The report says all 22,000 people who attended the festival that night are recognized as victims.

31 victims were pronounced dead at the scene. The rest were pronounced dead at medical facilities they were taken to afterward. Police have previously said that 58 people died in the attack.

• Investigators have chased 1,965 leads in the case. They've also reviewed more than 21,000 hours of footage and issued 1,062 legal notices during the investigation.

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Revelations about the gunman

• Investigators recovered "several hundred images of child pornography" on Paddock's hard drive. The investigation into the images in ongoing, the report says. The investigation into the images in ongoing, the report says. CNN previously reported that Paddock's brother was charged with possession of child pornography.

• Paddock's doctor believed he may be bipolar. According to the report, Paddock's physician described him as "'odd" in behavior with "little emotion' shown." Though he believed Paddock could have had bipolar disorder, Paddock "did not want to discuss that topic further with him." Paddock refused anti-depressants but accepted prescriptions ordered for anxiety.

• He was described as "germaphobic." Paddock also claimed multiple times to friends or family that he "felt ill, in pain or fatigued," the report said.

• Paddock paid off all his gambling debts before the shooting. It's already been reported that Paddock, a notorious gambler, was completely funded by his gambling habits and real estate transactions.

• Paddock's demeanor changed over the last year. His girlfriend, Marilou Danley, told investigators he had become "distant," the report says, "and their relationship was no longer intimate."

• The shooter's girlfriend believed buying guns was a hobby for Paddock. The 64-year-old purchased 55 firearms between October 2016 and September 2017, the report says. All of the guns recovered in the Mandalay Bay, with one exception, the report says, were purchased after September 2016.

Photos: Mass shooting at Las Vegas music festival Debris is scattered on the ground Monday, October 2, at the site of a country music festival held this past weekend in Las Vegas. Dozens of people were killed and hundreds were injured Sunday when a gunman opened fire on the crowd. Police said the gunman fired from the Mandalay Bay hotel, several hundred feet southwest of the concert grounds. It is the deadliest mass shooting in modern US history. Hide Caption 1 of 30 Photos: Mass shooting at Las Vegas music festival Broken windows of the Mandalay Bay are seen early in Las Vegas on Monday. Police said the gunman fired on the crowd from the 32nd floor of the hotel. Hide Caption 2 of 30 Photos: Mass shooting at Las Vegas music festival People cross a street near the Las Vegas Strip just after sunrise on Monday. Thousands were attending the music festival, Route 91 Harvest, when the shooting started. Hide Caption 3 of 30 Photos: Mass shooting at Las Vegas music festival People embrace outside the Thomas & Mack Center after the shooting. Hide Caption 4 of 30 Photos: Mass shooting at Las Vegas music festival Police arrive at the Sands Corporation plane hangar where some people ran to safety after the shooting. Hide Caption 5 of 30 Photos: Mass shooting at Las Vegas music festival A woman cries while hiding inside the Sands Corporation plane hangar. Hide Caption 6 of 30 Photos: Mass shooting at Las Vegas music festival Concertgoers dive over a fence to take cover from gunfire on Sunday night. Hide Caption 7 of 30 Photos: Mass shooting at Las Vegas music festival Police take position outside the Mandalay Bay. Hide Caption 8 of 30 Photos: Mass shooting at Las Vegas music festival A man lays on top of a woman as others flee the festival grounds. The woman reportedly got up from the scene. Hide Caption 9 of 30 Photos: Mass shooting at Las Vegas music festival Hide Caption 10 of 30 Photos: Mass shooting at Las Vegas music festival People are seen on the ground after the gunman opened fire. Hide Caption 11 of 30 Photos: Mass shooting at Las Vegas music festival People run from the festival grounds. Hide Caption 12 of 30 Photos: Mass shooting at Las Vegas music festival A woman is moved outside the Las Vegas Tropicana resort. Multiple victims were being transported to hospitals in the aftermath of the shooting. Hide Caption 13 of 30 Photos: Mass shooting at Las Vegas music festival People are searched by police at the Tropicana. Hide Caption 14 of 30 Photos: Mass shooting at Las Vegas music festival An ambulance leaves the intersection of Las Vegas Boulevard and Tropicana Avenue. Hide Caption 15 of 30 Photos: Mass shooting at Las Vegas music festival A man in a wheelchair is evacuated from the festival after gunfire was heard. Hide Caption 16 of 30 Photos: Mass shooting at Las Vegas music festival Victims of the shooting are tended to in the street. Hide Caption 17 of 30 Photos: Mass shooting at Las Vegas music festival Concertgoers help an injured person at the scene. Hide Caption 18 of 30 Photos: Mass shooting at Las Vegas music festival People gather around a victim outside the festival grounds. Hide Caption 19 of 30 Photos: Mass shooting at Las Vegas music festival A couple huddles after shots rang out at the festival. Hide Caption 20 of 30 Photos: Mass shooting at Las Vegas music festival An injured woman is helped at the Tropicana. Hide Caption 21 of 30 Photos: Mass shooting at Las Vegas music festival Police and emergency responders gather at the intersection of Las Vegas Boulevard and Tropicana Avenue. Hide Caption 22 of 30 Photos: Mass shooting at Las Vegas music festival A police officer takes position behind a truck. Hide Caption 23 of 30 Photos: Mass shooting at Las Vegas music festival A crowd takes cover at the festival grounds. Hide Caption 24 of 30 Photos: Mass shooting at Las Vegas music festival Police officers advise people to take cover in the wake of the shooting. Hide Caption 25 of 30 Photos: Mass shooting at Las Vegas music festival People tend to a victim at the festival grounds. Hide Caption 26 of 30 Photos: Mass shooting at Las Vegas music festival Police stand at the scene of the shooting. Hide Caption 27 of 30 Photos: Mass shooting at Las Vegas music festival A woman sits on a curb at the scene of the shooting. Hide Caption 28 of 30 Photos: Mass shooting at Las Vegas music festival Police are deployed to the scene. Hide Caption 29 of 30 Photos: Mass shooting at Las Vegas music festival A man makes a phone call as people run from the festival grounds. Hide Caption 30 of 30

Report sheds light on how he planned attack

• Paddock behaved strangely during a stay at the Mandalay Bay a month before the shooting. Paddock had specifically requested rooms that overlooked the Las Vegas Village. Danley, his girlfriend, told investigators that during their visit she "observed Paddock constantly looking out the windows of the room that overlooked the venue. Paddock would move from window to window looking at the site from different angles." Authorities said they don't anticipate charges being brought against Danley, who has cooperated with investigators.

• Google search history shows Paddock researched other large-scale venues. This isn't necessarily new -- it was previously reported he booked hotel rooms overlooking Lollapalooza in Chicago. But the report reflects inquiries dating back to May 18, 2017. At that time, Paddock was mostly looking into venues in Boston.

The view of Las Vegas Village from Stephen Paddock's hotel room.

• Paddock googled "How tall is Mandalay Bay." Readers might remember that no suicide note or manifesto was found in Paddock's hotel room. The only piece of paper in the suite contained calculations the gunman made to determine how far his bullets would drop based on the height of his room, and the distance between himself and the venue. Paddock may have used the height of the hotel to calculate the trajectory.