When a crime has just been committed, the accused is usually arrested without warrant. It is called warrantless arrest. If the offense committed has a penalty of at least 4 years, 2 months and 1 day, (e.g. murder, rape, etc.) a complaint or information may be filed by a prosecutor without need of preliminary investigation provided an inquest has been conducted in accordance with existing Rules. (sec. 7, Rules of Court)
An inquest is "a summary inquiry conducted by a prosecutor for the purpose of determining whether the warrantless arrest of a person was based on probable cause."
While a preliminary investigation is a proceeding distinct from an inquest. A preliminary investigation is "an inquiry or proceeding to determine whether there is sufficient ground to engender a well-founded belief that a crime has been committed and the respondent is probably guilty thereof, and should be held for trial." (IMELDA S. ENRIQUEZ vs. JUDGE OLEGARIO R. SARMIENTO, JR. , A.M. No. RTJ-06-2011,