Investigators probing whether someone else was staying in Las Vegas gunman's suite

Investigators in Las Vegas are combing through evidence to determine whether another person was staying with the gunman, Stephen Paddock, who carried out the deadliest mass shooting in modern U.S. history on Sunday.

NBC News reports investigators have found a phone charger that does not match any of the cellphones owned by Paddock. They also one of his key cards was used to get into his room during a period when his car had left the parking garage.

The report comes as Thursday investigators are looking for a woman they say accompanied Paddock in the days leading up to the shooting.

“I want to emphasize we believe Paddock is solely responsible for this heinous act,” Las Vegas Metropolitan Police Department Asst. Sheriff Todd Fasulo said Thursday. “We are aware of the rumors outside of the media and also on social media that there was more than one assailant. We have no information or evidence to support that theory, or that rumor. We believe there was only one shooter and that was Stephen Paddock.”

Still, in a press conference on Wednesday, Clark County Sheriff Joe Lombardo told reporters investigators are operating under the assumption Paddock was assistant by someone.

“On face value, you have to make the assumption that he had to have some help at some point,” Lombardo said. “And we want to ensure that that’s the answer.”

Paddock on Sunday killed 58 innocent people at the Route 91 festival on the Las Vegas strip. The Las Vegas Review-Journal on Tuesday reported he also shot up two aviation fuel tanks during the roughly 9-minute assault, and may have planned subsequent attacks. Paddock reportedly booked a hotel room overlooking the Chicago musical festival Lollapalooza, and had previously scouted sites in Boston.