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.
Investigators are still trying to determine why Paddock committed the deadliest mass shooting in modern US history.
He killed 58 people and wounded hundreds of others last Sunday before taking his own life.
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Earlier on Saturday US Vice President Mike Pence spoke on Saturday afternoon at a prayer service in Las Vegas honouring the 58 victims killed last Sunday.
Pence says those killed were taken before their time. But he says, "Their names and their stories will forever be etched into the hearts of the American people."
Fifty-eight doves were released outside on the steps of City Hall. They flew in a wide arc before disappearing into the distance as someone shouted, "God bless America!"
Investigators are still trying to figure out what led Paddock to carry out the attack.
