Answer:
If a rape kit was collected, and DNA is found on an item or from bodily fluids, a DNA test can be performed years or even decades later. Many criminals ― some even on death row ― were exonerated from crimes they were falsely found guilty of before DNA testing was available. Once the technology was available, irrefutable DNA evidence freed the wrongly accused.
Additionally, if a baby resulted from the rape, a DNA test can confirm who the father is.