An acquaintance of mine also ran into something similar with the local law enforcement where I live. They threw him in jail for 24 hrs for "speeding and reckless driving" in the police station parking lot (which has surveillance) because he did not wait another two hours to file a complaint against a neighbor (police crony) for harassing his son. An officer stated that he witnessed the whole thing. They stormed his house with 4 officers 4 hours after the incident, through him up against the wall in front of his terrified daughter to arrest him. Come trial, the police video was "lost" or "deleted". Luckily, the much more tech savvy fire department next door had their surveillance video and graciously provided their video footage exonerating said person.
They do not "lose" them. They intentionally delete them to leave no trail which can be used against them in trial or congressional oversight committee.
Always remember, the prosecution is a human as well as the defense attorney and both will bend the truth to their liking in order to show that something/nothing wrong was done.
BTW, the attorney for the acquaintance humiliated the police department in trial who then had to issue a formal apology.