I'm Doug, and I'm very sorry to hear of your son's situation. My goal is to provide you with excellent service today.
While it is a matter of proof, there is in fact a WA statute that actually sets out a viable defense to child rape---when the adult reasonably believes that the minor is of legal age and that reasonable belief is based on specific statements made by the alleged victim.
Here is the statute: RCW 9A.44.030 (2) In any prosecution under this chapter in which the offense or degree of the offense depends on the victim's age, it is no defense that the perpetrator did not know the victim's age, or that the perpetrator believed the victim to be older, as the case may be: PROVIDED, That it is a defense which the defendant must prove by a preponderance of the evidence that at the time of the offense the defendant reasonably believed the alleged victim to be the age identified in subsection (3) of this section based upon declarations as to age by the alleged victim.
You might want to reconsider the private attorney, as they seem to understand the process here and they may be able to avoid the harsh effect that a conviction of this particular charge could bring.
Here is a link to the law: http://apps.leg.wa.gov/rcw/default.aspx?cite=9A.44.030
And, here is a link to an article on this defense:
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I wish you the best in 2013,