• Mr. Paddock complained often to friends and family members about pain and fatigue. But the doctor who had been his primary care physician since 2009 said that the only major ailment he had was from a slip and fall at a casino in 2013, when he tore a muscle. The doctor told investigators that Mr. Paddock was “odd” and showed “little emotion.” While he believed Mr. Paddock may have had bipolar disorder, Mr. Paddock refused to discuss it or take antidepressants, though he did accept anti-anxiety medication. Mr. Paddock often refused to take medication, he said.

• Over more than three decades — from 1982 through the fall of 2016 — Mr. Paddock bought 29 firearms, including handguns, shotguns and one rifle. Such purchases accelerated beginning in October 2016: He bought more than 55 firearms in less than a year, mostly rifles. He also bought more than 100 firearm-related items such as scopes, ammunition and bump stocks in the year before the attack.

• Ms. Danley told investigators that Mr. Paddock’s demeanor changed during the last year — he became “distant” and “their relationship was no longer intimate.” He became “germaphobic” and had strong reactions to smells. During a stay at the Mandalay Bay in early September, Ms. Danley said he had behaved strangely, and constantly looked out the windows of the room and at the concert venue below from different angles.

• Mr. Paddock appeared to begin thinking about a mass shooting last May, searching on Google for “summer concerts 2017” and “biggest open air concert venues in USA.” In early September he searched for “Las Vegas high rise condos rent” and “life is beautiful expected attendance,” a reference to another large outdoor concert in Las Vegas that month. Two weeks later, he looked for “swat weapons,” “ballistics chart 308,” “SWAT Las Vegas,” and “do police use explosives.”