The gunman that opened fire on a Las Vegas music festival scouted locations in Boston and Chicago to carry out attacks, NBC News reported on Thursday, citing senior law enforcement officials briefed on the matter.

One of Stephen Paddock's potential targets included the Lollapalooza music festival in Chicago's Grant Park in August, according to the report. He booked a hotel room in the city, but never showed up.

Paddock, 64, also looked into hotels in Boston near Fenway Park, NBC News reported.

There is no evidence that he traveled to either city.

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Paddock opened fire on the Route 91 Harvest Festival in Las Vegas on Sunday from the 32nd floor of a nearby hotel. The attack killed at least 58 people and injured more than 500 others.

Paddock was found dead after SWAT teams stormed his hotel room.

Law enforcement is also looking into whether Paddock rented several units in a high-rise building overlooking another music festival held the weekend before he carried out the attack on the Route 91 Harvest Festival.

Investigators are still searching for a motive behind the attack and are trying to determine why Paddock researched locations in Boston and Chicago, according to NBC News.

FBI agents questioned the Paddock's girlfriend, Marilou Danley, on Wednesday, after she returned to the U.S. from a trip to the Philippines, where she was reportedly visiting family. She has said that she had no knowledge of Paddock's plan.