Motive behind Vegas music festival massacre remains a mystery: Authorities

The FBI still has an ongoing case against someone tied to the shooting, police said.
1:47 | 01/20/18

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Transcript for Motive behind Vegas music festival massacre remains a mystery: Authorities
In the meantime, major developments in the investigation after the massacre in Las Vegas, the largest mass shooting in modern U.S. History. We have never before seen images from inside that hotel room and what the girlfriend has now revealed. Here's ABC's Clayton Sandell tonight. Reporter: Tonight new images from inside a hotel room turned sniper's nest. A staggering number of rifles strewn on countertops, chairs, beds, the floor. Hundreds of shell casings and a hammer next to glass from the shattered window where Stephen paddock opened fire. Targeting a crowded Vegas music festival below, murdering 58 people, injuring more than 700. Get down, get down! Reporter: For more than three months, authorities have provided few details about the deadliest mass shooting in U.S. History. Today the sheriff released a report he calls "Preliminary." I've lost a lot of sleep over this. Reporter: But after chasing nearly 2,000 leads since October, the gunman's motive is still a mystery. They police say he acted alone. He had lost a significant amount of his monetary wealth in close proximity to 1 October and that may have a driving factor associated with it. Reporter: The sheriff says he does not expect charges against paddock's girlfriend who had told investigators he had become distant and withdrawn over the last year and began buying more guns. The day before the shooting the gunman twice drove from the mandalay bay from his home returning with at least six suitcases. When police used explosives to below open his hotel room door, paddock was already dead. He believed that we were in close proximity of engaging him and he decided to T his own life. Reporter: Tonight the sheriff says the FBI still has an ongoing case against someone connected to the shooting but he's not saying who that is or why. Thank you.

This transcript has been automatically generated and may not be 100% accurate.

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