Las Vegas gunman Stephen Paddock booked rooms in a Chicago hotel facing the Lollapalooza music festival in August, a law enforcement official told USA TODAY on Thursday.

Paddock, 64, booked one room at the Blackstone Hotel starting Aug. 1, two days before the festival opened. He booked a second room Aug. 3. The Blackstone confirmed in a statement that rooms were booked in Paddock's name during Lollapalooza but that he did not stay there on those dates.

Both rooms had a checkout date of Aug. 6, corresponding with the final day of the music festival that drew tens of thousands of concertgoers to Grant Park alongside Lake Michigan. It was unclear if Paddock was in Chicago during the festival, according to the law enforcement official, who was not authorized to discuss the case publicly.

The lineup for the festival included artists Lorde, Chance the Rapper and Arcade Fire. Among the attendees at the festival was former President Obama’s daughter, Malia. Some 100,000 people turned out each day for the event, according to local media.

“We are aware of the media reports and have been in communication with our federal partners,” the Chicago Police Department said in a statement. “As you saw earlier this week the city conducts extensive public safety planning and training around major events, in close coordination with our law enforcement partners, to ensure public safety."

In addition to Paddock’s bookings in Chicago, a federal law enforcement official says the gunman also expressed interest in Boston in the past several months, prompting authorities to notify local authorities there. Paddock appeared to be interested in hotels in the vicinity of Boston’s Fenway Park, but whether the interest corresponded with events at the iconic ballpark was not immediately clear.

In a statement, Boston FBI chief Harold Shaw said authorities “are assessing evidence to determine a motive.”

“Without commenting on specific evidence, we understand information may come to light that we are pursuing to determine its relevance,” he said. “We will not speculate and will make final determinations when we have all of the facts.

The official, who was not authorized to comment publicly, said Thursday that information referencing other locations is being drawn from investigators’ continuing analysis of Paddock’s communications devices.

Although investigators believe the digital and physical trail Paddock left in his wake is crucial to resolving his motive for the attack, the official cautioned that the information recovered — including his interests in locations beyond Las Vegas — have so far not led authorities to any firm conclusions.

Investigators looking into Paddock's background and his movements before his killing spree erupted in Las Vegas say he must have had some help along the way given his huge arsenal and precise plans, but they have no idea who that might be.

While Clark County Sheriff Joseph Lombardo suggested that Paddock may have had a plan of escape following his assault, the federal official said the gunman had limited options, even though he had rigged surveillance cameras to monitor the outside hallway of his hotel room.

By the time heavily armed Paddock, dug in on the 32nd floor of the Mandalay Bay, would have been alerted to trouble outside, the official said the gunman would have been boxed in.

Investigators believe Paddock was the sole gunman, but authorities are actively attempting to determine if others provided assistance, either wittingly or unwittingly. “You have to make the assumption that he had some help at some point,” Lombardo said.

Tracking his recent movements, investigators are examining surveillance cameras at gun stores, restaurants and hotels to determine if others accompanied him.

Paddock's girlfriend, Marilou Danley, 62, said in a statement that she had no idea what he was planning or why.

Danley, who was in the Philippines when the shooting occurred, flew back to the United States and is cooperating with authorities.

“He never said anything to me or took any action that I was aware of that I understood in any way to be a warning that something horrible like this was going to happen,” Danley said in a statement read by her lawyer outside FBI headquarters in Los Angeles.

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Paddock lived a low-key, private life, including spending hours playing highstakes video poker in Las Vegas casinos. He was such a steady customer that hotels gave him free rooms, including one on the 32-second floor of the Mandalay Bay casino overlooking a country music festival.

The wealthy real estate investor opened fire Sunday from his multistory perch onto the crowd below, killing 58 people and injuring nearly 500. He then shot and killed himself as police tried to break into the room.

Investigators trying to determine what triggered the massacre say Paddock's plans were meticulous.

Las Vegas authorities confirmed Wednesday that Paddock had rented a room at Las Vegas’ Ogden hotel the week prior, during Life is Beautiful, a three-day music and arts festival. Investigators haven’t determined whether Paddock was considering targeting the festival, Lombardo said. Investigators were expected to review footage from cameras at the Ogden during his stay to see if they could glean any clues, he added.

Paddock also amassed a huge arsenal of weapons and explosives, and set up surveillance equipment outside his room to detect any approaching outsiders, including police.

Investigators say he also had a plan to survive the shooting and try to escape, though would not say how.

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Even the No. 2 official in the FBI said Wednesday he was surprised investigators have not uncovered more about why a man with no obvious criminal record would cause so much bloodshed.

“There’s all kinds of things that surprise us in each one of these events. That’s the one in this one, and we are not there yet,” FBI Deputy Director Andrew McCabe said. “We have a lot of work to do.”

“This individual and this attack didn’t leave the sort of immediately accessible thumbprints that you find on some mass casualty attacks,” McCabe said. “Putting aside the somewhat dubious claims of responsibility that we see in each one of these instances, we look for actual indicators of affiliation, of motive, of intent, and so far we’re not there. We don’t have those sort of indicators.”

Investigators analyzing Paddock’s computer, cellphone and other electronic devices have found no obvious ideological motive, no clear connection to extremists or activist groups or outward display of mental illness.

Paddock wired $100,000 to the Philippines before the shooting, a federal law enforcement official, who was not authorized to comment publicly, told USA TODAY.

Danley, who was overseas for more than two weeks, said she was initially pleased when she was wired money from Paddock to buy a house for her family in the Philippines. But she later feared it was a way to break up with her.

She said she loved Paddock as a “kind, caring, quiet man” and hoped they would have a future together. Danley added she was devastated by the carnage and would cooperate with authorities as they struggle to get inside Paddock’s mind.

Contributing: Kevin Johnson; The Associated Press