IIUC, most/all jurisdictions in the US, and i'm not sure if this is statutory law or common law, is that a "finder" of "abandoned property" is required to notify police of the find. in most cases the police will then take the property into custody and wait for it to be claimed... if it's not claimed it will be sold at auction. i'm not aware of the finder having any legal rights to take possession; especially if the "found" object is secured with a lock.

"finding" a bike that's locked to a (semi-)publicly accessible rack, destroying the lock, and selling the bike = theft. it would have to be there for much more than a month before a property manager can claim otherwise, unless there's a clause on the lease that states other terms, or conspicuous and properly maintained signage near the rack.

it might be different if your bike was locked to a sign, stair-rail, etc... the property manager could then claim that it's an obstruction or safety hazard, but he'd still have to keep it safe for a reasonable time or deliver it to the police.

btw, did you have the serial number of the bike? did you report it as a theft? it would be amusing if the landlord sold it to a pawn shop and the police can pursue it that way. it almost sounds like s/he just wanted your bike, and attempted to make stealing it sound legitimate.