CHICAGO (CBS) — A misunderstanding about an active shooter drill at a downtown building led to police being called for, what they thought was, the real thing.

It happened around 10:30 a.m. Wednesday morning at the Monroe Building at 104 S. Michigan Ave. WBBM’s Bernie Tafoya reports.

“They forgot to say it was a drill,” said Lisa Luttenegger who works in the building; so people believed there was an active shooter in the building.

According to Luttenegger, employees went to their assigned shelter locations, but police were called by people who thought it was a real thing.

“Police came and made us leave the building,” Lettenegger said.

As for what she would like to say to building management?

“Thanks for the heart attack,” Lettenegger said. “A lot of us were a little scared.”

Property Manager Paul Rades said there was no miscommunication, only that people were not paying attention.

“We alert our tenants ahead of time,” Rades said. “They’ve known about this weeks and weeks ago.”

Rades said tenants were told, weeks ago, that the plan was to have an active shooter drill, in which people shelter in place, followed by a fire drill in which everyone meets in the lobby.

He promised a further statement later to come Wednesday.

Alex Lang, who also works in the building, had a message for building management.

“Let’s just try to do better next time,” Lang said.