I read an article a year or so ago about a prosecutor who, once DNA evidence revealed that the defendant (convicted prior) was innocent started theorizing that he was one of two rapist, but wore a condom.

So yeh. There are no limits and no meaningful rules as to what they can and will do. Certainly many feel no moral or ethical constraints on their actions.

And what actually ended up happening in that situation? Did the DA take the defendant to trial under that theory?

I think he's referring to the case of Roy Criner. What was ridiculous is that I remember watching a documentary that focused in part about this case and they interviewed the district attorney who was denying an appeal of the case after the DNA analysis of the semen confirmed that it didn't belong to Roy Criner. The DA was adamant that he was obviously guilty because he was given a fair trial and that the DNA evidence just meant that the victim also had sex with someone else recently before she was raped and murdered by Criner.

http://www.law.northwestern.edu/legalclinic/wrongfulconvicti... http://www.pbs.org/wgbh/pages/frontline/shows/case/etc/updat...