Bicycle detail

We store our bikes on the lower floor of our open air apartment building. We had locked our two bikes together and locked them to the railing of the small enclosure where we were storing them. I noticed late on the night of July 29th when I returned home and was walking up the stairs that it looked down on the lower floor like there was only one bike. Upon going down and checking, the bikes had been unlocked somehow and the Marin mountain bike had been taken. The other (cheaper) bike was still there. I don’t consciously check on the bikes every day but I do look down the stairwell every time I go up to our apartment and believe I would have noticed very quickly when it went missing. For that reason I believe it was sometime this past weekend (July 27th-29th). I’m unsure of the exact model but will try to locate that info. It is a dark gray bike with black shocks in the front.