Hmmmmmmmmm, so you are tellling me that a completely innocent person would plant his semen to lead the investigation away from the real perpetrator?????????
I don't think you would plant your own semen. Obviously this kind of evidence planting would have to be done by someone with access to semen samples and the victim's body. I once read a crime novel where the bad guy, a serial rapist, got hold of a fresh, discarded, used condom and he planted that semen on a few of his victims. The results were devastating for the guy who discarded the condom.