Chicago Police were on the scene at NBC's street side studio this morning investigating a broken window on the east side of the building.
Security guards on patrol at the time said they were there when they heard the sound of glass shattering.
They rounded the corner and saw no individuals there. One security guard, who declined to be named, said there was a visible hole in the window before the glass began crumbling.
Authorities suspect a projectile of some sort was propelled through the window from elsewhere.
This is a developing story. Stay tuned for more information.