Powell was convicted last month of 14 counts of voyeurism. The standard sentence would be about four years in prison.
The News Tribune reports prosecutors filed a notice saying he deserves 10 years to hold him accountable for crimes against both girls.
The 62-year-old will be sentenced June 15 in Tacoma.
Powell is the father-in-law of Susan Powell, who disappeared from her home in West Valley City, Utah, in late 2009. His son - her husband - Josh Powell killed himself and two sons in a February fire at a home in Graham.
Information from: The News Tribune
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