Authorities in the US are investigating the possibility that the Las Vegas gunman planned more attacks, including a car bombing, a US official has said.
Investigators are also looking into whether Stephen Paddock scoped out bigger music festivals before killing 58 and injuring 489 when he opened fire on Route 91 Harvest Festival on Sunday night.
The 64-year-old booked rooms overlooking the Lollapalooza festival in Chicago in August and the Life Is Beautiful show near the Vegas Strip in late September, investigators have said.
They continued that it is not yet clear if he aborted plans to carry out massacres at those sites.
Authorities also came across mention of Fenway Park, Boston police spokesman Mike McCarthy said.
Investigators had previously disclosed that the multi-millionaire had 1,600 rounds of ammunition in his car, along with fertiliser that can be used to make explosives and 50 pounds of Tannerite, a substance used in explosive rifle targets.
The weekend before Sunday's massacre, Paddock rented a room through Airbnb at the Ogden condominiums in Las Vegas and stayed there during a music festival below that saw performances from Muse, Lord, Blink-182 and Chance the Rapper.
"Reasons that ran through Paddock's mind is unknown, but it was directly at the same time as Life Is Beautiful," Sheriff Joseph Lombardo said.
Police have been reviewing video shot at the 21-storey apartment block to check Paddock's movements.
They believe his decision to rent one of the flats is strange because as a high-stakes gambler, he could easily have got a free room at one of the casino hotels on the Vegas Strip.
Meanwhile in early August, Paddock booked a room at Chicago's 21-storey Blackstone Hotel that overlooked the park where the Lollapalooza alternative music festival was being held, however, the hotel confirmed he never checked in.
Despite their findings, authorities say they still have no idea of Paddock's motives, although the FBI said they do not believe it was terrorism.
The profile developed so far of the former accountant is of a "disturbed and dangerous" man who acquired an arsenal of 47 guns over decades, Sheriff Lombardo said.
He continued that investigators have been frustrated to find that he lived a "secret life... much of which will never be fully understood".
Although Paddock killed himself as a Swat team closed in after he had carried out the deadliest mass shooting in modern US history, the sheriff said it appeared he had planned to survive and had an escape plan.
The latest developments announced by the authorities come as America's powerful National Rifle Association (NRA) called for devices that turn semi-automatic rifles into fully automated weapons - such as those used by Paddock - to be "subject to additional regulations".
Twelves of the rifles found in the hotel room used by Paddock were reportedly modified with a "bump stock" attachment, allowing them to fire faster.
However, while there have been renewed calls for tighter gun regulations in the US in the wake of the massacre, the NRA - which holds a powerful sway over members of Congress - argued that: "Banning guns from law-abiding Americans based on the criminal act of a madman will do nothing to prevent future attacks."