motion detection

There must be some kind of animal living in our apartment or sneaking in through the window because I keep noticing chucks being bitten off my little basil plants as well as disturbance in the soil. One day there was about a 5 inch hole in the soil that appeared out of nowhere and the soil had been tossed around. They are growing in a large barrel on a closed-in balcony, near a window. I am planning on setting up a webcam and motion-detection software tonight to try and catch the culprit.