Investigators believe a note found in the Las Vegas shooter's hotel room contained a series of numbers that helped him calculate more precise shots.
A law enforcement official said on Saturday that the numbers found on a note on a nightstand included the distance between the high-rise hotel room that Stephen Paddock was using as a perch and the concert the victims were attending.
The official wasn't authorised to discuss the details of the investigation publicly and spoke to The Associated Press on condition of anonymity.
As Las Vegas police are appealing to the public for help in uncovering a wealthy retiree's motive for massacring 58 people at an outdoor concert this week, US Vice President Mike Pence has visited Las Vegas offering solace.
"We are united in our grief, in our support for those who have suffered and united in our resolve to end such evil in our time," Pence said on Saturday, joining Las Vegas Mayor Carolyn Goodman and other local leaders at a City Hall commemoration for victims of the shooting that followed a prayer walk through the city.
Participants trod 11km along four separate paths to City Hall for an event where security was high. President Donald Trump paid a visit to Las Vegas earlier in the week.
The commemoration came as Clark County Undersheriff Kevin McMahill said investigators remain largely in the dark about what drove retired real estate investor and high-stakes gambler Paddock to carry out the deadliest mass shooting in modern US history.
McMahill said investigators had uncovered "no nexus" between Islamic State and Paddock, even though the militant group had repeatedly claimed responsibility for the attack.
In an unusual bid to cast a wider net for tips, the FBI and police have arranged with communications company Clear Channel to post billboards around Las Vegas urging citizens to come forward with any information they believe might help investigators.
The billboards will bear the slogan, "If you know something, say something," and carry a toll-free number to an FBI hotline, said Aaron Rouse, special agent in charge of the Las Vegas FBI office.
Paddock, 64, unleashed a torrent of gunfire onto an outdoor music festival from the windows of his 32nd-floor hotel suite overlooking the concert on Sunday night, then shot himself to death before police stormed his room.
In addition to the 58 people who died, nearly 500 were injured, some by gunfire, some trampled or otherwise hurt while running for cover.
Unlike so many other perpetrators of deadly mass shootings before him, Paddock left behind no suicide note, no manifesto, no recordings and no messages on social media pointing to his intent, according to police.