There are reports that Paddock had booked rooms in Chicago facing a music festival held there. So, he planned for a while different locations with large crowds where he could kill mass amounts of people. Also that he was researching attack sights in Boston. He planned out his mass murder, knowing that it would be easier for him to do because of his access to assault rifles.
Also the fact that he was planning to attack in Chicago, be knew that bringing in guns which he got from states with more lax gun laws, would overcome Chicago's attempts to crack down on people murdered by guns. And those who bring up Chicago's murder rate to counter the debate whenever gun control is brought up. One man was able to kill 59 and injure nearly 500 others within minutes. As high as all of the people of get shot/killed/injured in a week in Chicago. Don't use the high murder rates in Chicago, if they are willing to call one person being able to commit mass murder. with a assault rifle. "The price of freedom."