This is an archived article and the information in the article may be outdated. Please look at the time stamp on the story to see when it was last updated.CHICAGO — Thousands are expected to pack the four-day Lollapalooza festival this weekend, after it kicked off in Grant Park Thursday morning. Mayor Lori Lightfoot promised a “robust security plan,” as city leaders work around the clock to keep people safe. Lightfoot’s promise came Monday, a day after a shooting at a California food festival that killed three people and wounded 12. Chicago’s Office of Emergency Management and Communications notes in a statement that tighter security measures are implemented each year, including measures both seen and unseen. In addition to the fencing around the park, 330 security cameras have been put in place, 900 private security guards on the ground, plus a vast number undercover and uniformed cops patrolling the park and surrounding neighborhoods. While tickets typically sell out to the festival, some are still available as of Thursday evening. Thursday’s headliners are the Chainsmokers.