I think the prosecuting attorney is going for exactly what they could win today. Aggravated Murder in Washington State is the charge that carries the death penalty. There are extenuating circumstances for this, and in this case he would be eligible for Agg. 1st Degree if there was another element of the crime (rape, kidnapping, etc.) My sense is, they will up the charges when (and if) they can prove more.
There is some misreporting as to the 21-28 year sentence. This is a minimum sentence up to life in prison. Washington has a complicated formula for sentencing guidelines that uses a matrix and calculation to show what sentencing range the convicted person would be eligible for. This means that the identical crime could carry different sentences based on the history of the offender. Google Wa State Sentencing guidelines and you'll most likely get a link for the calculator that is used. For this reason, though, there is not a clear cut sentencing range quite yet....and there are other factors that add to the sentence (sexual motivation and firearms for instance).
