Interesting question. If someone is engaged in conduct rising to the level of what you refer to as a "peeping tom", the conduct should be reported immediately. If there are facts and circumstances that make one think about it, I'm wondering what those facts and circumstance are and what is going on.
This answer is provided for informational purposes only. Actual legal advice can only be provided in an office consultation by an attorney licensed in your jurisdiction, with experience in the area of law in which your concern lies.
Mr. Myers answer is the correct one. Regardless of the statute of limitations, "peeping tom" conduct should be reported immediately.
However, generally in Alabama the statute of limitations on a misdemeanor is 12 months and the statute of limitations on most felonies is 3 years.