I am a cop who had done background investigations. Everything you mentioned is available to an investigator, regardless of what you were told. Community service and monetary fine means that you were guilty. I don't know the specifics of your state, but here my applicants (and I when I applied to each of my prospective cop jobs) are required to sign a form authorizing the agency to get copies of "confidential" paperwork. You basically sign away your privacy rights when you go into this background investigation.
The general consensus is also correct. A squeeky clean candidate is so infrequent that it arouses suspicion. Everyone has something in thier past where they may have technically violated a law. I was barred from employment at one location for a juvanile prank that other agencies really don't care about.
We cannot get a pool of perfect applicants. We look for patterns of behavior. A pattern of behavior shows you don't learn well. Our applicants are human, and will have problems. DWI, Domestic Violence, and felony convictions are automatic disqualifiers by state law. All other run ins are looked at on a case by case basis.
I have never done drugs. Ever. That is a rarity in todays world, and it earned me a hell of a time on the polygraph, not because I was dishonest, but because the polygrapher thought I was beating the machine. Just because the machine says you are telling the truth doesn't mean that you are. My job was in jeopardy because the polygrapher thought I was beating the machine and he launched into two hour interrogation to find out if I was lying.
After four years of trying to get hired, I did. Different agencies rejected me for different reasons, only one failed me during the background investigation/polygraph. I wanted to be a big city cop, and I was applying in big cities. The applicant pool was rather large, and they had no reason to process what might be a "marginal" applicant when there are more, better qualified persons already in the process.
It is not that bad to make a mistake. It is not bad to make an error of judgement. It is very bad to lie and try to cover it. An officer that I know was fired in a situation were he was commiting a misdemeanor crime, one that we investigate daily, and take action on after a lenient warning. (basically this crime is a petty misdemeanor, and when we come into the situation we warn. Many people get breaks on this one). He would have recieved a substantial suspension, and possible reassignment, but he would have kept his job IF he had come clean. He lied. He was fired. A rookie on probation was arrested in another state for a misdemeanor, and was honest. He kept his job, even though while on probation you can be fired for anything!
Also, it is human to want to hide things that make you look bad. It is natural. If you don't have the courage to be honest (and face the chances of not getting hired by that department), then you won't have the courage to chase down the felon running around trying to hurt people, either.
lemme pick up my soap box and I will go.
pat