Clark County Sheriff Joe Lombardo told reporters Monday that Paddock hid his actions in the time leading up to the shootings, which is making the process of seeking answers more difficult.
But he said local police officers are working with the Federal Bureau of Investigation and the Bureau of Alcohol, Tobacco and Firearms in the probe that involves behavioral analysts, repeat visits to Paddock's homes, analysis of his electronics and the ongoing work at the shooting site on the Las Vegas Strip.
'Currently we do not believe there is one particular event in the suspect's life for us to key on,' Lombardo said. 'We believe he decided to take the lives he did, and he had a very purposeful plan that he carried out.'
Investigators are talking with one of Paddock's brothers, as well as his girlfriend, about Paddock's movements and contacts during the time he would have been planning the attack as well as about his gun purchases.
Authorities have said they found 23 guns inside the Mandalay Bay hotel room where Paddock broke a window and fired on an outdoor country music concert across the street.
He also had substances in his car that could be mixed together to make explosives, as well as what Lombardo described as 'personal protection equipment' in the hotel room. The sheriff said there are indications Lombardo, who killed himself, had planned to escape as authorities responded to the attack.
Investigators have so far uncovered no evidence there was another shooter involved, nor that Paddock was linked to any known terrorist group or ideology.
Lombardo also announced Monday a change in the timeline of the October 1 shooting. He had said earlier that Paddock shot a security guard in the hallway of the hotel after firing on the concert, but now says the guard was shot first.