Bicycle detail

My apartment is located on a street with significant traffic during the day. There is an approximately seven (7) foot tall iron gate that requires a pin code to gain access to the stairwell leading to my apartment. Five (5) other apartments are located off of this stairwell. I usually lock my bike to the side of the stairwell (behind the locked iron gate). However, last night I forgot to lock my bike up. While I was at work, someone hopped over the approximately 5-foot tall brick wall onto the first-floor patio of my downstairs neighbor's apartment, went out my neighbor's front door (which leads to the stairwell where I usually have my bike locked) and took my bike.