Thank you for your patience. Please be aware that the law on abandoned property in Washington State is very fact specific. They main thing that you want to do here is protect yourself. You cannot simply do with his property what you want. Also, although you say that you simply stored his belongings and he never lived with you, he may try to claim that he did and the laws involving a tenant's property are even more detailed and specific.
If the property has a value of less than $250, the law usually allows you to do with it as you wish - toss it or donate it, for example. However, you need to give the individual reasonable notice. In other words, you need to first mail him (through the US Postal Service, Certified Mail Return Requested) a letter informing him that he needs to make arrangements to pick up his belongings by X date or to have them moved. If the value is over $250, the law does require you to contact the Sheriff's Office after it has become clear that the property has been abandoned.
The main issue here is that if he has already accused you of things that are untrue, he might allege that he lived there with you where the property is and he would then have more rights and you would have to follow the law to a tee. The law you would need to follow if he was a tenant is as follows:
Under WA law, the tenant is required to specifically request that his items be stored. If you are considered to have been his landlord, you would need to prepare a Request for Storage of Personal Property form which the sheriff serves along with the writ of restitution. The tenant must complete and return the form to the landlord within three days. If the tenant fails to do so the landlord (you) has no obligation to store the tenant’s belongings.
If the tenant returns the notice to the landlord the landlord must store the belongings if the cumulative value is at least $250.00. The belongings may be stored in the rental property.
The landlord must then give notice of intent to sell the personal property to the tenant’s last known address. After the thirty days expire the landlord may sell all the property – including family pictures, personal papers, and keepsakes, and dispose of any items not sold.
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