Investigators still have not found a motive for the Las Vegas shooting rampage that killed 58 people, Undersheriff Kevin McMahill has said.
The Clark County official said the authorities have looked at gunman Stephen Paddock's personal life, political affiliation, economic situation and any potential radicalisation.
He said investigators are aware the Islamic State group has claimed responsibility for the attack, but so far there is no evidence that it had a role.
Mr McMahill said the authorities will continue to investigate those areas as well as look into leads and tips that come in.
Paddock unleashed gunfire on Sunday from the 32nd floor of the Mandalay Bay hotel casino on the Las Vegas Strip, killing 58 and injuring nearly 500 people.
He killed himself as police closed in.
The authorities are planning to put up billboards in Las Vegas to seek more tips as they investigate the deadliest mass shooting in modern US history.
Mr McMahill revealed at a news conference on Friday that police are confident there was not another gunman in Paddock's room, and do not have any information that anyone else used his room key.
He said they are interested in Paddock's medical history and are looking into that.
Paddock, 64, fired indiscriminately from his upper-level room at the Mandalay Bay hotel casino at people attending a country music festival below.
It had emerged earlier that investigators are looking into whether Paddock scoped out bigger music festivals in Las Vegas 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.
It was not clear if he contemplated massacres at those sites.
The investigation 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.
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.
The profile developed so far is of a "disturbed and dangerous" man who acquired an arsenal over decades, Sheriff Joseph Lombardo said.
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 demeanour. 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.