In what circumstances will the prosecution be successful in compelling a witness to attend trial?

In People v. Mendieta (1986) 185 Cal.App.3d 1032, the appellate court held the prosecution failed to exercise due diligence in compelling a witness's attendance for trial when at or about the time of the preliminary hearing the witness had advised the chief investigating officer he would be leaving the state, but the prosecutor made no attempt to serve the witness a subpoena before his departure and no attempt was made to secure his attendance under the Uniform Act. (Id. at p. 1036.) The witness corroborated the only other evidence of the defendant's guilt, namely, the victim's identification testimony; he was the "only 'neutral' witness" who placed the defendant at the crime scene; and there was no physical evidence; accordingly, the error was not harmless beyond a reasonable doubt. (Id. at p. 1039.)