Are you and/or your wife represented by an immigration attorney? If not, then you may wish to hire an attorney to make status inquiries on your behalf so that you do not have to continue to do so. As well, USCIS and ICE do NOT disclose when they are doing investigations, so simply being told there is no investigation may or may not be accurate.
While I know it is frustrating, your options are somewhat limited to pressure the USCIS to make a decision. If the case is FAR beyond the reported processing times (usually a year or more beyond), then a federal court mandamus action might result in a decision. However, it is important to be aware that it also will result in a detailed review of the case, and that in some jurisdictions, it provokes USCIS into looking for a reason to issue a denial rather than an approval.
Although not likely to be of any comfort to you, when I started practice (which wasn't all that long ago), immediate relative adjustment of status cases often were taking over three years to process! There has been improvement, although there certainly is room for more.
If you do need assistance locating an experienced immigration attorney to assist you with status inquiries or advise about mandamus, you can look here on Avvo, at www.aila.org, or www.ImmigrationLawHelp.org. Hopefully, though, you will receive your decision very soon if the case review truly is complete.
Ms. Doerrie's answer to your question is general in nature, as not all facts and circumstances relating to the specific person(s) and situations involved are known to her. Ms. Doerrie recommends consulting with an immigration attorney regarding your specific facts and circumstances prior to making any legal decision or submitting any form or application. This response does not create an attorney/client relationship.
I agree with my colleagues in that it is not possible to decide if the delay is caused by an administrative issue (reassigned agent, delayed security clearance, etc) or something more seriosu such as a superior officer finding that evidence gathered by the agent who interviewed can result in the AOS being denied. You can request an INFOPASS to the local office and request an update on your application. That way you may be able to headoff any problem and get a Request for Evidence rather than a Denial Notice. If there is a problem or issue you should contact an experienced immigration attorney for a legal opinion as to how to progress.
Legal disclaimer: The statement above is provided by CC Abbott is based on general assistance and not intended to be a legal opinion because not all the facts are provided. The person requesting information and all others reading the answer should retain an attorney who is permitted by the state bar within the jurisdiction who can examine the complete facts and provide a legal opinion on your case. All information provided in the above answer and other information provided by CC Abbott does not create an attorney/client relationship within any state of Federal law.