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Investigators trying to piece together why a gunman opened fire on a crowd of thousands of concert-goers in Las Vegas this week said they have chased down more than a thousand leads, but the motive in the deadliest mass shooting in modern U.S. history remained a mystery.

"I believe we will have an answer. But that answer may also end up being 'we don't know why he did it,'" Las Vegas Metropolitan Police Department Undersheriff Kevin McMahill said in an interview Friday, five days after Sunday's shooting that left 58 people dead and hundreds wounded. McMahill added investigators will continue to work diligently to try and determine a motive.

Stephen Paddock, 64, opened fire from the 32nd floor of the Mandalay Bay Resort and Casino onto as crowd of thousands at a country western concert Sunday night. Authorities said he apparently killed himself as police closed in.

McMahill said at a press conference that the over a thousand leads had "helped create a better profile into the madness of this suspect" although officials still do not have "a clear motive or reason why."

Authorities say they have found no link to international terrorism. The terror group ISIS, without providing any evidence, claimed responsibility for the attack but the claim has been widely discounted.

"In the past, terror attacks or mass murder incidents, motive was made very clear — very clear in most of those cases by a note that was left, by a social media post, by a telephone call that was made, by investigators mining computer data," McMahill said at Friday's press conference.

"Today, in our investigation, we don't have any of that uncovered. I wish we did," he said. "We will, and are, continuing to investigate with great tenacity, and hope to arrive at an answer."

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Paper with numbers on it found in the shooter's room are believed to be calculations of shooting ranges, drops, and distance for higher precision in shooting into the concert crowd, multiple law enforcement sources familiar with the investigation told NBC News Saturday.

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Also Friday, McMahill said police are confident that Paddock was the only shooter, and that no one entered the hotel room before the shooting.

Earlier, law enforcement sources said investigators were puzzled by a charger that did not appear to match any of Paddock's cellphones. Police have now been able to match all of the cell phone chargers found in the room with multiple cell phones that Paddock had with him.

Authorities continue to investigate whether anyone knew about Paddock's plans.

"The execution piece of this, we're confident he did it alone," McMahill said. "But did anybody else know what he was planning, and why? And that is a main focus of our investigation today."

Police are looking at "everything" about the shooter, including finances, personal life, political affiliation and social behavior, McMahill said.

McMahill said they also found approximately 50 pounds of tannerite and ammonium nitrate — materials that can be used to make explosive devices — in the gunman's car, but it did not appear that Paddock had assembled the material into an improvised explosive device.

Law enforcement officials briefed on the investigation also said Friday that they had learned Paddock approached an ammunition dealer wanting to buy a large quantity of tracer rounds at a gun show in Phoenix last month.

The dealer did not have the quantity Paddock wanted, so the shooter did not end up buying anything from him, they said. The dealer told law enforcement that Paddock was neatly dressed and polite, and did not say anything that would raise a red flag. He gave the dealer the impression that he wanted the tracer rounds for recreational use with friends.

Law enforcement learned of the encounter because Paddock had an ammunition box bearing the dealer’s name.

Senior law enforcement officials said Paddock had researched possible attack locations in Boston and Chicago, including the Lollapalooza festival in Chicago in August.

Samantha Faranda of Las Vegas, who was shot four times, returned home Friday.

"I'm just grateful that I didn't have to completely say goodbye to all the people that I love," she said. "And I just — I’m really lucky."