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The gunman who massacred dozens in Las Vegas researched possible attack locations in Boston and Chicago, multiple senior law enforcement officials briefed on the investigation told NBC News.

Stephen Paddock's potential targets included the most recent Lollapalooza festival in Chicago, which was held Aug. 3 to Aug. 6 in Grant Park, the officials said. Paddock, 64, went as far as booking a room in a Chicago hotel but did not show up, the officials said. Among the thousands of people who attended the festival was Malia Obama, daughter of former President Barack Obama.

Paddock also did online research on hotels around Boston's Fenway Park, a senior law enforcement official with direct knowledge of the matter said. Most hotels in the area, however, have an obstructed view of Fenway — or no view at all.

The FBI and Boston police have been in touch since Wednesday on information tying Stephen Paddock's web searches to the city, Boston law enforcement officials said.

And Boston Police Commissioner William Evans has talked to Boston Red Sox officials to ensure that playoff games this weekend would have extra police resources in and around the ballpark. Some of those resources will be visible and some of those resources will be undercover, the official said.

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The Boston Police said in a statement that there was no threat to any venue in the city, including Fenway Park.

Officials also said that Paddock searched for the Boston Center for the Arts.

There is no indication Paddock ever traveled to Boston or Chicago, the officials said.

The officials stressed that investigators still do not know Paddock's motive behind the Las Vegas shooting, in which he fired from a 32nd floor hotel room onto a country music festival Sunday night, killing 58 people and injuring 489. Investigators are trying to understand what the Chicago and Boston research was all about.

Related: Las Vegas Gunman Stephen Paddock Kept Firing for 10 Minutes, Police Say

Authorities are also investigating whether Paddock rented several units at a luxury high-rise overlooking a bigger music festival, called Life Is Beautiful, the weekend before Sunday's slaughter, a law enforcement source said.

Paddock, who lived in Mesquite, Nevada, fired on the crowd of 22,000 for about 10 minutes, and killed himself as police closed in on him, authorities have said. Police are still trying to determine whether he had any help or whether anyone knew about his plans.

Clark County Sheriff Joe Lombardo said he thought the gunman probably did have some kind of assistance, because he had prepared an elaborate escape plan that would have been difficult to execute by himself.

Photos: Harrowing Photos Show Moments After Vegas Massacre

Investigators have interviewed Marilou Danley, Paddock's girlfriend, who returned to the United States from the Philippines, her homeland, where Paddock had sent her two weeks earlier. She told investigators that she had no clue what Paddock was planning, her attorney told reporters on Wednesday.

Investigators found material used to make exploding targets in containers in Paddock's car, along with about 1,600 rounds of ammunition, Lombardo said.