Investigators are looking into whether Las Vegas gunman Stephen Paddock scoped out bigger music festivals in the city and Chicago before Sunday’s massacre.

Paddock booked rooms overlooking the Lollapalooza festival in Chicago in August and the Life Is Beautiful show near the Vegas Strip in late September, according to authorities reconstructing his movements before he undertook the deadliest mass shooting in modern US history.

It was not clear if he contemplated massacres at those sites.

Investigators looking into Paddock also came across mention of Fenway Park – home of the baseball side the Boston Red Sox – Boston police Lieutenant Detective Mike McCarthy said, though he provided no further details.

The details came to light as detectives struggled to figure out why the high-stakes gambler opened fire on a crowd of 22,000 from the 32nd floor of the Mandalay Bay hotel casino in Las Vegas. on Sunday night.

He killed 58 people and injured nearly 500 before taking his own life.

A federal official said authorities are looking into the possibility Paddock planned additional attacks, including a car bombing.

Authorities previously disclosed Paddock had 1,600 rounds of ammunition in his car, along with fertiliser that can be used to make explosives and 50 pounds of Tannerite, a substance used in explosive rifle targets.

Map locates shooting in Las Vegas(PA graphic)

Investigators combing through his background for clues remain stumped as to his motive.

The profile developed so far is of a “disturbed and dangerous” man who acquired an arsenal over decades, Sheriff Joseph Lombardo said.

Authorities are looking into the possibility Stephen Paddock planned additional attacks (Eric Paddock via AP)Authorities are looking into the possibility Stephen Paddock planned additional attacks (Eric Paddock via AP)

But investigators have been frustrated to find that he lived a “secret life,” Mr Lombardo said, “much of which will never be fully understood.”

A former executive casino host at the Atlantis Casino Resort and Spa in Reno said Paddock had a “god complex” and expected quick service without regard to how busy the staff was at the time.

“He liked everybody to think that he was the guy,” John Weinreich said. “He didn’t boast about anything he had or anything. It was just his demeanor. It was like, ‘I’m here. Don’t cross me. Don’t look at me too long’.”

Meanwhile, Las Vegas police announced on Thursday they had found a Hyundai Tucson they had been searching for as part of the probe while executing a search warrant at the home in Reno that Paddock shared with his girlfriend, Marilou Danley.

Paddock had an arsenal of 23 weapons in his hotel room. A dozen of them included “bump stocks,” attachments that can effectively convert semi-automatic rifles into fully automated weapons.

In a rare concession on gun control, the National Rifle Association announced its support on Thursday for regulating the devices.