Bicycle detail

The last time I had my bike, I had it parked in one of the available outdoor bike parking spaces adjacent to my apartment (the one nearest to the traffic lights/crosswalk/sidewalk). It was surrounded by other bikes that were parked next to it. I used a U-lock to secure it. Before heading to bed, I went downstairs again to my bike at approximately 12:50 AM to retrieve the battery of the bike to charge for tomorrow. The whole bike was still there at that time, secured by the lock. In the morning around 9:35 AM, I headed downstairs with the fully charged battery with the intention to put it back, but the bike was no longer there. The only thing left behind was the U-lock locked onto the rail where my bike used to be. I guessed that it had been stolen as I made sure that it was secure last night. The incident likely occurred between from when I took out the battery to when I went outside to use it again (1 AM- 9 AM, Jan 26th). As the bike parking is directly next to my building and adjacent to an intersection on the road, I assumed that there might have been security footage. As of now, I still have the keys to turn on the bike, as well as the battery and U-lock