Speculating here, but presumably the victim is willing and able to supply their own DNA as an elimination sample. Whatever DNA is left over gets run through a

Speculating here, but presumably the victim is willing and able to supply their own DNA as an elimination sample. Whatever DNA is left over gets run through a database, and possibly matched with an identity. If the identity comes with a photo, the victim may well be able to verify whether that photo is that of their attacker.