what happens here at corvallis police headquarters when you find that out?sort of an amazing day. that's the smoking gun. that's the nail in the coffin. narrator: the wilbergers returned to corvallis to get the news themselves. and they said, we got a dna confirmation that brooke's dna and his dna were in the van together. did you break down? no, you know, you just-- you get up for certain things. you're-- you just steel yourself for that. and it was like, yes, you know? and then-- and then i-- of course, i sobbed the whole way home. narrator: the dna evidence had revealed details no mother should ever have to hear and no witness had yet disclosed. it was the nature of the dna evidence, which told an even bigger story. narrator: benton county, oregon district attorney john haroldson. the dna evidence was in the form of bodily fluids, which were co-mingled. that told us a story, in terms of what had occurred in that van. narrator: the co-mingled dna indicated brooke had been raped. so joel courtney was charged with that crime, in addition to kidnapping and mu

because everybody knows about it, says to him you need to call corvallis police department. e does. kate snow (voiceover): coming up, it was not just police asking questions about brooke's case. so was the suspect's own sister. there were some similarities. and so you thought to yourself-- could it be? no. i mean, you couldn't even say the whole sentence because it was unthinkable, right? kate snow (voiceover): when "dateline" continues. narrator: joel patrick courtney was sitting