So this is a great question and Im honored you asked for my opinion.
@Barry. Per usual this will probably be long (sorry guys the law is nothing if not long-winded). I looked at Colorado requirements and found:
Colorado statute § 16-5-209. Judge may require prosecution:
The judge of a court having jurisdiction of the alleged offense, upon affidavit filed with the judge alleging the commission of a crime and the unjustified refusal of the prosecuting attorney to prosecute any person for the crime, may require the prosecuting attorney to appear before the judge and explain the refusal. If after that proceeding, based on the competent evidence in the affidavit, the explanation of the prosecuting attorney, and any argument of the parties, the judge finds that the refusal of the prosecuting attorney to prosecute was arbitrary or capricious and without reasonable excuse, the judge may order the prosecuting attorney to file an information and prosecute the case or may appoint a special prosecutor to do so. The judge shall appoint the special prosecutor from among the full-time district attorneys, assistant district attorneys, or deputy district attorneys who serve in judicial districts other than where the appointment is made; except that, upon the written approval of the chief justice of the supreme court, the judge may appoint any disinterested private attorney who is licensed to practice law in the state of Colorado to serve as the special prosecutor. Any special prosecutor appointed pursuant to this section shall be compensated as provided in
section 20-1-308, C.R.S.
If a judge finds a reason to appoint a special prosecutor they usually choose district attorneys, assistant district attorneys, or deputy district attorneys that currently work in nearby jurisdictions. So theoretically the only potential additional costs of appointing a SP would be the cost of lodging or travel for that SP, and its likely that cost would be minimal if they choose a SP that's practicing near the area.
Looking at the decision notes I also found:
Disqualification of a DA - Occurs when DA Asks to Be Removed From A Case
Disqualification of a district attorney in a criminal prosecution is proper only when: (1) the district attorney requests his or her own disqualification; (2) the district attorney has either a personal or financial interest in the prosecution; or (3) special circumstances exist that would make it unlikely that the defendant would receive a fair trial.
People v. Lincoln, 2007, 161 P.3d 1274
Situations Warranting Appointment of a Special Prosecutor
Court will appoint special prosecutor when it is shown that district attorney's decision, either to prosecute or not to prosecute, was motivated by bias or personal interest; evidence must show that district attorney will either reap some benefit or suffer some disadvantage and mere partiality will not suffice.
Sandoval v. Farish, 1984, 675 P.2d 300.
Standard of Evidence Needed
District judge should not, in absence of
clear and convincing evidence that terms of statute pertaining to appointment of a special prosecutor have been met, substitute his judgment or discretion for that of prosecutor in a criminal case.
Tooley v. District Court In and For Second Judicial Dist., 1976, 549 P.2d 772, 190 Colo. 468.
Factors Considering When Reviewing A Prosecutors Charging Decision
In reviewing prosecutor's charging decision, court may consider following factors: likelihood of convictions; sufficiency of evidence; availability of witnesses in corroboration of offense; credibility of victim; evidence relating to motive or intent of offender; seriousness of injuries inflicted; competing demands of other cases on time and resources of prosecutor.
Sandoval v. Farish, 1984, 675 P.2d 300.
Who Has Standing to
The ordinary citizen does not have a general interest justifying a lawsuit based on the criminal prosecution or nonprosecution of another.
Dohaish v. Tooley, 1982, 670 F.2d 934, certiorari denied
103 S.Ct. 60, 459 U.S. 826, 74 L.Ed.2d 63.
To determine if standing exists, a court must consider whether a plaintiff was injured in fact and whether the injury was to a legally protected right.
Peters v. Smuggler–Durant Mining Corp., 910 P.2d 34, 38 (Colo.App.1995),
aff'd, 930 P.2d 575 (Colo.1997). With respect to the latter requirement, “[a] complaining party may show injury to a legally protected right by demonstrating that the harm allegedly suffered is protected by a statutory or constitutional provision, or by a judicially created rule of law that entitles the complaining party to some form of judicial relief.”
Sender v. Kidder Peabody & Co., 952 P.2d 779, 781 (Colo.App.1997).
In our view, all three considerations support the construction of section 16–3–108 as not authorizing private citizens to seek arrest warrants. We hold this view for the following reasons:
1. Most law enforcement officers (i.e., police officers, sheriff's officers, and district attorneys' and the attorney general's investigators) are certified peace officers whose very job it is to investigate crime. See §§ 16–2.5–102, 16–2.5–103, C.R.S.2010. All of those officers are experienced at investigation, and are trained to prepare affidavits and to know the meaning of probable cause and how to apply it. Most lay people are not so experienced or so trained.
2. Law enforcement officers are subject to additional employment sanctions besides those associated with criminal charges for perjury if they lie or recklessly disregard the truth in an affidavit. Most lay people are not subject to such employment sanctions.
3. Law enforcement officers are, ideally, objective investigators with no stake in the outcome of a case, and thus, they evaluate the information that they receive without bias. Such objectivity is not presumed from lay people who are “involved” in cases.
Kailey v. Chambers, 261 P.3d 792, 798–99 (Colo. App. 2011).
Given the amount of time, effort, and resources local LE has put into the case I don't think they would likely stay silent if the DA choose not to prosecute, especially given the publicity of this case. All that being said, Im still a law student and I have no experience with Colorado courts, so this analysis is my best guess based on the current statutes and the notes on the decision. If anyone would like further explanation of any part of my Special Prosecutors dissertation please let me know lol