A police officer's testimony and credibility can be examined and/or questioned just like anyone else. Speak with an attorney who can review your case files and determine whether or not you have any claims.
A gun law attorney is best-suited or this matter. The pending trespass case may be a factor in Court as evidence of his prior/current criminal record/history. Most likely he was charged with an intermediate-level felony. An attorney may help him reduce or eliminate his charge(s).
Generally six years from the breach of promise. The type of promise made may affect the time limit so if the statute of limitations is a concern of yours then I recommend speaking with a New York contracts attorney in a confidential forum as soon as possible.