Defendants in criminal cases have the right to confront and cross-examine the witnesses against them. Allowing the police officer to testify as to what a non-appearing witness told him would violate the defendant's right to confront and cross-examine that witness. With very few exceptions, this is not permissible.
Furthermore, the statements of a witness to a police officer which are recorded in a police report would be hearsay if offered into evidence at trial and would, with some exceptions none of which would appear to apply here, be inadmissible for that reason.
In criminal cases, there are usually no pre-trial depositions. There are some limited circumstances under which a sworn statement may be taken from a witness (such as when the witness is dying and will not survive until the trial) and used at trial. If the defendant has already been charged, this will be done with attorneys for both sides present. If no defendant has yet been identified, it can be done by the prosecution alone and perhaps used at trial (after a big fight against it by the defense attorney).
If a witness testified in some previous hearing in the criminal case (such as a preliminary hearing in a felony) and the prosecution can demonstrate that the witness is unavailable to testify at trial, despite diligent efforts to secure the attendance of the witness, the preliminary hearing testimony may be admissible.
Police officers can testify only to what they saw and what physical evidence they gathered. Generally speaking, they cannot testify to what is in their police reports unless their original testimony is impeached in some way and the report can rehabilitate the testimony; or, if they cannot remember some detail which is otherwise admissible, they can use the report to refresh their recollection or to read from as a "past recollecton recorded".