CHICAGO (CBS) — A woman was sexually assaulted in a parking garage in the South Loop early Tuesday morning, police said.

Police were called at 3 a.m. to the 1100 block of South Delano Court, where they found a 35-year-old woman standing in the garage. The officers tried to speak to the woman, but she was so traumatized she did not respond, police said.

A man who was a witness told officers that he had seen another man leaving the garage, and the witness went on to say that the woman had approached him and told him she had been raped in the lower level of the garage, police said.

Officers again tried to speak to the woman who this time said she had been approached by man who had taken out a gun, beaten her, and then raped her.

Security cameras were being reviewed Tuesday afternoon. Area Three detectives were investigating.