Bicycle was left locked during the workday and stolen sometime between approximately 09:00 and 18:00. Bicycle locked to rack with Kryptonite New York Lock (one of the sturdier available U-locks) through the frame. Other bicycles of comparable value are left there. Rack is normally full during the workday. Location is well trafficked and well lit during the day, when the theft occurred. Lock was found still attached to the rack, and did not appear to be compromised. Because it is unlikely the thief picked the lock, removed the bicycle, and then relocked the lock onto the rack, suspected means of theft are either (1) user attached the lock to the rack but not to the bicycle, which enabled thief to simply walk away with bicycle or (2) the thief cut through the frame. Both seem strange. (1) is unlikely because use has been bicycle commuting every day for years and has not once failed to include the bicycle within the U-lock. Locking a bicycle is something one concentrates on while doing it, and it's hard to not apply the lock to the bike and not notice. (2) seems unlikely because locking the frame (vs the wheels only) is considered safe because sawing the frame would considerably diminish the value of the bicycle. In theory someone skilled may be able to TIG-weld the aluminum back together, though it would likely be apparent repair had been performed.