Question regarding an "abandoned" residential rental property.

My in-laws own a home in Snohomish County and it appears to have been abandoned. Both the water and power have been shut off for non-payment, and the tenant has failed to return phone calls. They also have not paid for the past 2 months. Do we have to post a pay or vacate notice, or are we entitled to enter the property now since it clearly has been abandoned. Also, they have left personal property in the home, and a broken down truck in the driveway.