A letter of apology to customer regarding loss of an item in its custody. It offers compensation or replacement of the item, and provides explanation of the loss made.
Please accept our sincere apology for the loss. There is no excuse for such carelessness and please confirm with us if there is anything that we can do to replace or compensate you for the loss. The incident is an isolated case that rarely happens in [our premises / facility] [and we take full responsibility for the loss].
We are reviewing our process to institute corrective measures to avoid this type of loss in the future.