This is a complicated issue. Generally, if the items have been abandoned, they may be discarded. HOWEVER, "abandonment" can be a hotly contested issue, and if the person that moved out claims the items were not abandoned, that they didn't really move out, or that they intended to move back in, they might have claims against the remaining tenant for theft, unlawful eviction or other causes of action. This could be the case even if the person who moved out was not on the lease. Colorado's eviction statute can provide a shield against this type of liability, so it's a good idea to speak with an experienced eviction attorney in determining a course of action.