Oct. 6 (UPI) -- Police in Las Vegas said Friday that they are "confident" Stephen Paddock was the only shooter targeting concert goers in Sunday's massacre.
Clark County Undersheriff Kevin McMahill gave a briefing dispelling speculation otherwise.
"We're very confident there was not another shooter in that room," he said.
Unnamed senior law enforcement officials told NBC News earlier in the day that a charger that didn't match any of Paddock's cellphones or other devices, was found in the room, leading them to question whether someone else might have been there.
Clark County Sheriff Joe Lombardo on Wednesday had said, "You've got to make the assumption he had to have some help at some point."
McMahill said police still aren't sure whether anyone else knew about the attack before it happened.
Meanwhile, police said they found the vehicle owned by shooter Stephen Paddock, and an explosive compound called Tannerite inside the car.
The SUV, a Hyundai Tucson, was found while police executed a search warrant at Paddock's home in Reno, a police statement said late Thursday.
Authorities asked for help finding the vehicle soon after Paddock began his assault from a 32nd floor window at the Mandalay Bay Resort & Casino on the Las Vegas Strip Sunday night. His 10-minute shooting rampage on a country music festival killed 58 people and injured more than 500.
Tannerite was previously found in a car Paddock parked at the Mandalay Bay and in another of his homes, in Mesquite, Nev.
"I don't know what he was going to be doing with all that Tannerite. I wish I did and we're going to try to find out," McMahill said.
Police are still attempting to find a motive for the shootings.
"Usually there's a telltale sign associated with these types of actions -- reclusive, a plethora of things associated with this mindset -- and we have not found that yet," Lombardo said.
A candlelight vigil in Las Vegas' Police Memorial Park attracted thousands of people on Thursday evening. It honored Charleston Hatfield, 34, a Las Vegas police officer who was shot to death during the assault.
Authorities have not disclosed why Paddock may have possessed the explosive material, since no bomb was used in the attack. They said they also found ammonium nitrate, another ingredient that can be used to make explosives, in his vehicle in Las Vegas.
Fallout from the shooting dominated a security meeting of Las Vegas law enforcement and security personnel on Thursday. The open design of the city's main casino area has long been regarded by security experts as a potential target, the Nevada Independent reported. Immediately after the shooting, several casinos began scanning guests and checking luggage more closely.
The attack, the deadliest in U.S. history, is regarded as an anomaly by some law enforcement officials, unlike most mass shooting incidents -- which experts say are typically confined to a closed space.