A disgruntled former employee shot and killed two men in a “targeted attack” at Navy Pier in Chicago, according to authorities.

Chicago police responded to calls of an “active shooter” around 1:18 p.m. Tuesday after a man stormed the popular tourist attraction and fired “multiple shots” at two people, Police Chief Jon Hein said.

The unnamed shooter is believed to be a former employee who had worked as a subcontractor on the dock and knew how to gain access to the rear loading area, Hein added.

Once inside, the gunman allegedly targeted two men in a “private office area.”

The victims – both men aged 47 and 51 who also worked for a contractor – were shot in the head.

Both were rushed to Northwestern Memorial Hospital, where they succumbed to their injuries, Hein said. Lamont Johnson, 51, was later identified by the coroner’s office as one of the victims.

Navy Pier, which has 70 different tenants, was closed immediately after the shooting.

At the time of the attack, many families had visited the attraction, CBS News reported. Trent Halasek, of Cincinnati, Ohio, told reporters he was visiting the pier when he saw officers “in full riot gear and SWAT gear” coming down.

Police said the suspect had already fled the scene.

Hein said the suspect has now been identified as a former worker whose employment contract was terminated on October 14.

Navy Pier Operations Officer Brian Murphy said the attack was a targeted “isolated incident” and that no one else on the pier was in danger. It is unclear if the weapon was recovered from the scene.