In Arizona, the statute of limitations on felony charges is 7 years. (For some special cases, like first degree murder, it is indefinite.) However, if your nephew is being held on a secured $75K bond, and has a public defender, it sounds like the charges have already been filed. Once charges are filed, your nephew has special rights called Speedy Trial Rights, which guarantee that if he is being held in custody that his trial (if there is no plea agreed upon) has to take place in a certain time frame. I discussed speedy trial rights on my blog (the link is below my name).
It sounds like the prosecution will have a tough time proving that your nephew is the guilty person. That all depends on the testimony of witnesses and if there is any tangible evidence (fingerprints, DNA, photographs, etc.).
Best of luck.