The gunman behind the mass shooting at an open-air festival in Las Vegas had reserved rooms overlooking music venues at other sites, investigators say.
Stephen Paddock is known to have booked a room during the Life is Beautiful festival in Vegas a week before he killed 58 people and injured hundreds.
But it has now emerged the retired accountant may have considered sites in Chicago and Boston.
Investigators are still trying to establish Paddock's motive.
A man named Stephen Paddock reserved a room at the Blackstone Hotel, in Chicago, at the same time as the Lollapalooza music festival was taking place in the Illinois city.
He never checked in, and a hotel spokesman said they had not confirmed "whether that is the same Stephen Paddock".
Among the revellers at the August festival were former President Barack Obama's daughters, Malia and Sasha.
The killing continues
By James Cook, BBC News, Las Vegas
Ask survivors of the Las Vegas massacre about gun control and you may well hear the sound of silence.
The cultures of country music and shooting overlap, and many concert-goers remain strong supporters of the right to bear arms.
"It's obviously kind of a touchy subject," singer and performer Krystal Goddard, 35, told me after recounting the horror of her escape from the gig.
"I think that guns are just a symptom of other things going on," she said, although she added that she did not understand why anyone needed to own an assault rifle.
There is some support among survivors for banning "bump stocks" but there is also a realisation that doing so does not amount to serious gun control.
And all the while the killing continues.
Fifty-nine people died here on Sunday. By Thursday afternoon at least 87 more people had been shot and killed across the US, according to the Gun Violence Archive.
That's a Las Vegas Massacre every three days.
The booking emerged after Clark County Sheriff Joseph Lombardo revealed Paddock had reserved another apartment in Las Vegas a week before Sunday's massacre.
The apartment was in the Ogden, a high-rise tower which, at the time, was overlooking another open-air concert, Life is Beautiful, where acts included Muse, Lorde and Chance the Rapper.
Meanwhile, The Boston Globe reports Paddock is known to have carried out internet searches for both Fenway Park and the Boston Center for the Arts, citing an anonymous government official.
Both venues have recently held open air events.
More than 100 investigators are combing through the life of Paddock, who has been described as "disturbed and dangerous", in order to find clues about why he committed Sunday's attack.
Sheriff Lombardo said Paddock had been "living a secret life, much of which would never be fully understood".
The gunman's girlfriend has also said she had no idea what he was plotting.
Police found the 64-year-old former accountant dead in a room on the 32nd floor of a hotel after he sprayed bullets on concert-goers below, injuring nearly 500.
He apparently turned one of his many guns on himself as police closed in.
In a press conference on Wednesday, Clark County Sheriff Lombardo was asked if he saw evidence that Paddock had planned to escape after the attack.
The sheriff said "yes". Asked what it was, he said: "I can't tell you."
He also revealed investigators had not entirely discounted the possibility the man they had initially described as a "lone wolf" may not have worked alone after all.
"You've got to make the assumption he had to have some help at some point," Sheriff Lombardo said.
"Maybe he's a super guy, maybe he was working out all this on his own, but it would be hard for me to believe that."