Before Stephen Paddock chose to attack the Route 91 Harvest festival in Las Vegas he may have considered carrying out similar massacres in other cities, including Chicago and Boston, NBC News reports.
"It was pre-planned, extensively, and I'm pretty sure that he evaluated everything that he did in his actions, which is troublesome", Lombardo said.
The police have said she is not a suspect.
Stephen Paddock, 64, turned a gun on himself on Sunday after firing hundreds of bullets into the crowd gathered for the final night of the Route 91 Harvest music festival, killing almost 60 people and wounding hundreds.
In the days after the Las Vegas mass shooting, more questions and speculations have been raised by investigators on the case. However, Lombardo and investigators did not identify any "person of interest" other than Paddock's girlfriend, Marilou Danley. Paddock did not check in to the room and it is unknown whether he was in Chicago that weekend, as first reported by TMZ.
He said that it was only logical to "make the assumption" that Paddock had "some help at some point" in pulling off Sunday's massacre, pointing to Paddock's huge arsenal, explosive materials found in his vehicle and his meticulous planning. "You have to make an assumption that he had help at some point".
Law enforcement says Paddock had stockpiled 47 guns since 1982 and bought 33 of them over the past year alone.
The Blackstone hotel also released a statement, saying the gunman specifically requested a "view room" that faced Grant Park.
Investigators found 23 guns inside Paddock's hotel room and 12 so-called "bump stock" devices that can enable a rifle to fire continuously.