Las Vegas gunman may have planned attack at Lollapalooza

LAS VEGAS -- The man behind the deadliest mass shooting in modern US history may have considered deadly attacks at the Lollapalooza festival in Chicago and an earlier festival in Las Vegas, investigators say.

Before checking into Mandalay Bay days before the massacre, Stephen Paddock rented a room at a Las Vegas condo complex that overlooked another music festival. Paddock rented the room at the Ogden condo complex via Airbnb during theĀ Life is BeautifulĀ music festival, which lasted from September 22 to 25, the sheriff said.

Continuing Coverage: Las Vegas Massacre

"Was he doing pre-surveillance? We don't know yet. This is all conjecture at this point," Lombardo said.

And in August, a person named Stephen Paddock reserved a room at Chicago's Blackstone Hotel during the city's Lollapalooza music festival, said Wagstaff Worldwide, which represents the hotel.

But that person never checked into the hotel, which overlooked the festival, WWM spokeswoman Emmy Carragher said.

It was not immediately clear whether the Stephen Paddock who booked the room was the same Stephen Paddock behind the Las Vegas massacre.

Wagstaff Worldwide said Blackstone Hotel is cooperating with authorities.

What motivated Paddock to kill dozens of strangers and whether he had help remains a mystery.

Law enforcement officials who have been briefed on the investigation told CNN on Thursday they have seen no indication that Paddock had an accomplice or that anyone was aware of his planning.