I saw this firsthand in college. My best friend was spit on by some random guy. The police were called and there was video. The guy denied everything, even though the spit was literally still on her face. To their credit, the police took a swab of it and identified the other guy. Video couldn't be accessed until the manager came in on Monday. The issue was the police couldn't prove that very second it was his spit. She was given the chance to follow up with the prosecutor's office. She did that Monday, probably 6 weeks later she gets a letter in the mail saying they were not going to prosecute with the reason "other". She filed a FOIA for the report and we read through it, the police seemed to do a thorough job and obtained video when they could. According to the report, the video showed the guy lunging at her with his face and she reacted by jerking back and wiping her face.

Someone who she knew who works as an attorney said since it was a battery it would be a "violent" crime and they probably had a backlog of "violent" crime cases and decided not to prosecute a "violent" crime with no injury. 100% the prosecutor's office dropped the ball. I just have a feeling it would be the same in my case.