You have done about all you can do. The officer will have to observe them in the violation or have a case based on strong enough evidence to win a conviction in court. Without additonal evidence even your testimony about seeing them shoot becomes a deal of your word against their word.
It is fairly easy to "know" somebody is violating. It is a much different story having the necessary evidence to convict them in court.
I would continue to funnel information to the officer and be patient while he/she uses that information to document a winneable case.
A written statement and willingness to testify is more than enough for an officer to make a case. You might not win the case but it still sends a strong message to the violaters. Even if their found guilty it's a very small fine and court cost. The message sent might be better than the conviction, plus the time spent in court and attorneys fees
You are certainly welcome to your opinion, but I totally disagree. I have never been much for taking a "wing and a prayer" case to court. IMO, you stand to lose more ground if you lose in court, and therefore a solid case is needed before prosecution.
Each to his own opinion, but you won't see many professional officers take a case to court where they don't have the evidence to get a conviction.