Yes, the DA, the Judge, and the Jury can all free the guy, and in case like this SHOULD free the guy. I said that like 4 times already. But still, the cop only needs an accusation from a witness to a crime to arrest him. That is all. Period. A witness is something that people involved in such things refer to as "Evidence". There are lots of other forms of evidence, but really, witnesses are the main type of evidence that they have in court. That's why they have a special place that they sit called the "Witness stand" and that's why they have all these silly ceremonies they go through like "swearing them in" and stuff like that.

As a mater of fact, whenever they have a piece of physical evidence, they are required to have, guess what? A witness to testify to the veracity of that physical evidence, a person who witnessed the collection, storage, and analysis of the evidence.

All evidence in court is based on witnesses.

Do you ever look at what happens in the real world?

"No. They need evidence, and even when they have evidence a person still gets arraigned before a judge who looks at the initial evidence and decides whether bail is necessary or if the person should just be released."

The judge (And DA) should look at the testimony of the witness and determine the bail, and whether charges should be pressed. Yes, exactly. AND THAT IS WHO FUCKED UP. Technically, the cops don't even need to know the law. They don't even need to have a high school education to be a cop, generally.

Is it a fucked up system? YES, absolutely. But that is what it is. the cop in this case will not get in one bit of trouble here, for the reasons above.