Police were searching for a lone gunman spotted outside the store by a witness, but said they had not identified him.

The victims were all found in the back of the Lane Bryant women's clothing store in an area not frequented by customers, Tinley Park Police Sgt. T.J. Grady told reporters.

Police confirmed that at least one of the victims was an employee of the Lane Bryant store, located at the Brookside Marketplace shopping centre in a southwestern suburb of Chicago.