There isn't any way that NiFong didn't know that there was semen present. It's a simple observation test using a specified light according to a web site I just read. DNA testing would be step 2 and require specialized lab work.
Absolutely inconceivable they would NOT test for semen so they did, he knew it was there and he knew there was no match. He held in from the defense (and public) and named these kids anyway. This guy is both a fool and very dangerous (to white people in the orbit of Durham)