Section 1. 

- It is an inquiry or proceeding to determine whether there exists sufficient ground to engender a well-founded belief that a crime has been committed and that the respondent is probably guilty thereof and should be held for trial.

1. To determine whether a crime has been committed and whether there is probable cause to believe that the accused is guilty thereof.
2. To preserve evidence and keep the witnesses within the control of the State.
3. To determine the amount of bail, if the offense is bailable.

Preliminary investigation is required to be conducted BEFORE the filing of a complaint or information for an offense where the penalty prescribed by law is at least 4 years, 1 months and 7 day without regard to the fine.

It is not part of the trial of the criminal action in court. Nor is its record part of the record of the case in the RTC. The dismissal of the case by the investigator will not constitute double jeopardy
and will not bar the filing of another complaint for the same offense, but if re-filed, the accused is entitled to another preliminary investigation (U.S. v. Marfori, 35 Phil 666).

It is subject to the requirements of both substantive and procedural due process.

The right of an accused to a preliminary investigation is not a constitutional but merely a statutory right. Nonetheless, it is a component part of due process in criminal justice and is a substantive

A personal right and may be waived expressly or by implication.

Lack of preliminary investigation is not a ground to quash or dismiss a complaint or information, nor does it affect the court’s jurisdiction. When there is no preliminary investigation, the accused must invoke it at the first opportunity and the court should hold in abeyance or suspend proceedings and remand the case to the office of the prosecutor for him to conduct PI.

1. Failure to claim it before the accused pleaded.
2. Silence of the accused
3. Failure to request it within 5 days from the time he learns of the filing of the complaint or information in those instances where the accused is lawfully arrested without a warrant.

Absence of preliminary investigation does not affect the jurisdiction of the court or invalidate the information if no objection was raised by the accused.

If an objection was raised, the court, instead of dismissing the complaint or information should order the conduct of such investigation (Doromal v. Sandiganbayan, 117 SCRA 354).

1. Refuse to enter a plea upon arraignment and object to further proceedings upon such ground.
2. Insist on a preliminary investigation.
3. Raise lack of preliminary investigation as error on appeal.
4. File a petition for certiorari.
5. File for petition for prohibition.

There is NO right of preliminary investigation when a person is lawfully arrested without a warrant unless there is a waiver of the provisions of Article 125 of the Revised Penal Code.

1. If a person is arrested, he can ask for preliminary investigation BEFORE the filing of the complaint/ information BUT he must sign a waiver in accordance with Article 125, RPC.
2. AFTER the filing of the information/ complaint, the accused may, within 5 days from the time he learns of its filing ask for preliminary investigation.

NOTE: This Rule has been partially amended by AM 05-0-8-26-SC. The amendments took effect on October 3, 2005. The amendment removed the conduct of preliminary investigation from the judges of the first level courts.