Contact your attorney immediately and give him/her this evidence. If it is what you say it is then he/she should be able to show it to the State and see what it could mean to your case. In my opinion NOBODY, not even prosecutors want injustice to happen.
It will be important to know how you came across the information. If the information was readily available to the defense prior to the trial, yet the defense did not use it, you likely have little to work with. However, if the information was not readily available and/or not made readily accessible by fault of the the prosecution, and such information should have been turned over as a part of pre-trial discovery, you may have a basis for bringing a motion for appropriate relief or a motion for new trial at some point. The thing to keep in mind, though, is that discovering/uncovering/etc. "new" evidence will not always affect the trial court outcome because, for example, if there is other good and valid evidence besides that which was not presented pointing to a Defendant's guilt, a Defendant might be out of gas when it comes to attempting relief as a result of new evidence not available at trial or uncovered afterwards through whatever means. The important thing is to immediately consult with your trial attorney about the evidence so that you all can discuss how it may or may not affect your rights presently.