You don't need DNA to convict. I still have no idea why these men were not convicted. You have not given any reason. If they confessed, why were they let out? There is something missing?
Did she lie and say she had not been with anyone else...because if she did, then yes, someone else's semem would seem to exonerate these men. If she admitted other sexual contact then it would not be exculpatory to find semen not of the accused.
The woman was killed in the incident.
I'll try to find the story now... It happened several years ago...