(CNN) -- Las Vegas shooter Stephen Paddock tried to buy tracer ammunition at a gun show in the Phoenix area in recent weeks, a law enforcement official briefed on the investigation tells CNN.
Paddock bought other ammunition at the show, but he couldn't obtain the tracer ammunition -- bullets with a pyrotechnic charge that, when the round is fired, leaves an illuminated trace of its path -- because the vendor didn't have any to sell, the official said.
Paddock did not use tracer bullets when he fired into the crowd at the Route 91 Harvest Festival Sunday night from his suite on the 32nd floor of the Mandalay Bay hotel, hundreds of yards away, killing 58 people and injuring hundreds of others.
The official explained that if Paddock had tracer ammunition, he would have had a more precise idea of where his shots were going in the darkness, and could have been more accurate.
In addition to the 23 weapons in his hotel suite, which he turned into a sniper's nest, Paddock had more than 50 pounds of explosive material and 1,600 rounds of ammunition in his car in the hotel parking lot, police said, fueling suspicion that he intended to survive the massacre.
"He was doing everything possible to see how he could escape," Las Vegas Police Sheriff Joseph Lombardo said, declining to detail specifics.
There was initial speculation that Paddock had outside help in perpetrating the shooting spree, but authorities now say there is nothing to suggest he had assistance.
Law enforcement officials briefed on the investigation told CNN they have seen no indication so far that Paddock had an accomplice or that anyone was aware of his attack planning.
Lombardo, the sheriff, had previously expressed skepticism that the gunman carried out his plan by himself.
"Do you think this was all accomplished on his own? You've got to make the assumption he had to have some help at some point," he said.
As the investigation grinds on, Las Vegas Metropolitan Police Department officers led the funeral of LVMPD officer Charleston Hartfield Thursday, who was among those gunned down at the Route 91 Harvest Festival country music event.
His body was escorted to Palm Downtown Mortuary and Cemetery, and a memorial was held for the slain police officer at Police Memorial Park in the northwest of the city -- one of several vigils in Las Vegas on Thursday evening.
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