Shadow activity can sometimes be easily debunked.
Look for windows where car lights can shine in, or people walking outside could cast a shadow, if needs be get someone to walk around outside & see if it can be recreated.
Mirrors can often cause this sort of optical illusion, with light bouncing around, it is quite easy to create strange illusions.
Another good idea is to get someone to drive around outside & see if the car lights can produce strange shadows.
Are there streelights nearby, could a bird or bat have flown past a window.