The district attorney has to be willing to press charges, or the arrest is pointless and just pisses off a 'partner agency' you have to 'cooperate with' to do your job. In most jurisdiction any citizen can effect an arrest, even vs a police officer (lol) but if the DA doesn't follow up with charges, you are looking at 'wrongful arrest' and 'unlawful imprisonment' as well as 'kidnapping' charges vs yourself since you don't have to legal immunity the police do preventing them from ever getting those charges against themselves.. someone just got off with a charge of 'impersonating a police officer' in my state, because under state law its illegal to claim you are a cop. even if you are a cop. there is no exemption in the impersonating law for the actual police, so the defendants attorney asked the judge to drop the case or he would place the testifying / arresting officer under citizens arrest for the same crime so they could be tried together, because the cop claimed to be a cop when he gave his testimony which was a violation of the same law he arrested the defendant for, since the way the law is worded in our state not even a cop can claim to be a cop legally. At that point if the court / da only pressed charges vs one of them he could effect a citizens arrest for deprivation of right under color of law, a federal crime, a felony, and turn them over for prosecution under federal courts.