I wonder whether it might be worth asking people again, now that the statute of limitations (or whatever the American equivalent is, if there is one) on statutory rape has passed? I can't imagine it would be a nice experience being asked about your girlfriend because she's dead and unidentified, and having to say "Nope, never seen her." Someone might be willing to talk if they know it is too late to get in trouble.
It's statute of limitations here, too. I think the statute is somewhere between 5 to 7 years depending on the jurisdiction, but I'm not 100% sure.