What is the test for a prosecutor to exercise due diligence in search and seizure of a witness?

While there is no universal formula to determine whether a prosecutor has exercised due diligence, courts look to the totality of the circumstances, including the character of the efforts made, whether the prosecutor reasonably believed the witness would appear willingly or if the prosecutor had reason to believe the witness would not, whether the search was timely begun, whether the witness would have been produced if reasonable diligence had been exercised (People v. Sanders, supra, 11 Cal.4th at p. 523) and how vital the witness's testimony is to the case (see People v. Hovey (1988) 44 Cal.3d 543, 564). The due diligence requirement is more stringent when the witness is vital to the prosecution's case and is one whose credibility is suspect. (Louis, supra, 42 Cal.3d at p. 991.) "Considerations relevant to the due diligence inquiry 'include the timeliness of the search, the importance of the proffered testimony, and whether leads of the witness's possible location were competently explored.'" (Herrera, supra, 49 Cal.4th at p. 622.) Good faith and due diligence do "not include pursuing futile acts not likely to produce the witness for trial." (People v. Hovey, supra, at p. 562.)