Following Sunday night’s (Oct. 1) massacre during a performance by country star Jason Aldean at the Route 91 Harvest Festival at the Mandalay Bay Resort in Las Vegas—now being called the deadliest such mass shooting in U.S. history—authorities looking through the killer’s electronic devices have reportedly discovered major concerts in other U.S. cities that he was potentially targeting.

News accounts report that the killer–whose name Best Classic Bands has chosen not to acknowledge–actually booked a hotel room in Chicago, which overlooks Grant Park where the 2017 Lollapalooza music festival was held. The room was apparently paid for but went unoccupied; this year’s event was held Aug. 2-5.

TMZ revealed that the man booked two rooms–as he did in Vegas–at the Blackstone, a luxury hotel on Chicago’s tony S. Michigan Ave. The Chicago Sun-Times quoted a source at the hotel who confirmed the booking. The festival attracts a crowd of well over 100,000.

Chicago PD spokesman Anthony Guglielmi noted, via Twitter: “We are aware of the media reports and have been in communication with our federal partners. The city is preparing for the Chicago Marathon which takes place this Sunday, Oct. 8, and will employ 1000 additional offers over and above what was initially planned.

CPD will have heavy undercover presence at this #ChicagoMarathon Well over 1,000 additional officers have been added to our deployment.

— Anthony Guglielmi (@AJGuglielmi) October 5, 2017

The killer’s electronic devices also revealed that he had been doing research of hotels in close proximity to Boston’s Fenway Park. While there are many hotels near the home of the Boston Red Sox, none have rooms that overlook the ballpark. Fenway hosted seven concerts this summer including a pairing of James Taylor and Bonnie Raitt, two shows by Dead & Company, and one by Billy Joel.