Were it you or I we'd certainly be put through the wringer. However, Charlotte Lloyd is not you nor I. She's the top model on the planet. If you look at the women who achieve that, they are uniformly worth hundreds of millions of dollars. She commands a massive media presence. The strength of legal representation that she can bring to the defense of the man that saved her and her daughter lives, from Zak Prince's killer, is beyond anything you or I can imagine. That legal representation by definition will be connected to the local and national power structure. All facets of law enforcement know this. The scrutiny over the investigation, evidence, witnesses, etc will be intensive. The lawyer(s) handling the case will be on a first name basis with the DA. The investigators employed by those lawyer(s) will have personal relationships with the investigating law officers. However unofficially or casually, they will be able to get "inside" how law enforcement is handling the case. Breaches in procedure will be known to the defense team as they happen, so they won't happen.
Plus this mess stinks. Carter was a murdering psychopath, who killed Zak, kidnapped Emma, held her at knife point (assault with a deadly weapon), assaulted the MC and attempted to murder him. Not every cop in Hillside is corrupt. Not every lawyer in the district attorney's office is corrupt. Emma is an innocent 18 year old girl, some members of law enforcement are going to have a difficult time with an attempt to rail road the man who saved her and her mother. Even the corrupt cops and officials can be influenced to "do the right thing" if there's a seven figure retirement plan in the end. Plus media coverage will make the OJ trial look like a park opening.
So your reasoning would apply to you or to me, but not in this case. In this case it's self defense, and in the real world it never gets to trial. Charlotte's lawyer(s) agree not to sue the city, and it ends with a conversation between the DA, the head detective, and the MC's lawyer who agree to dismiss any charges with prejudice and permanently close the case. Get it?