A warrant of arrest is not required in the following instances:
  1. When a complaint or information has already been filed pursuant to a lawful warrantless arrest (Sec. 5[c], Rule 112, Rules of Court). If the accused was lawfully arrested without a warrant, the prosecutor will only conduct an inquest proceedings. There is no need to issue a warrant because the accused is already under detention. The court will just issue a commitment order just to confirm the detention of the accused. 

  2. When a warrant has already been issued by the MTC judge pursuant to Sec. 5[b] of Rule 112 and the accused is already detained (Sec. 5(c), Rule 112). If the MTC issues a warrant of arrest and later on the case reaches the RTC, there is no need for the RTC to issue another warrant because there is already a warrant issued by the MTC. And as a matter of fact, the accused has already been detained.

  3. When the accused is charged for an offense punishable only by fine (Sec. 5[c], Rule 112). There are crimes where there is no penalty for imprisonment but only fine like damage to property through reckless imprudence. Based on the rules, there is no need for a warrant, just an order to appear is sufficient.

  4. In cases covered by the Rules on Summary Procedure (Sec. 16, 1991 Rule on Summary Procedure). The MTC will only issue a warrant of arrest if despite notice, the accused repeatedly absented himself during the trial.

  5. In cases not requiring a preliminary investigation. If the MTC judge finds probable cause but is satisfied that there is no necessity for placing the accused under custody, he may issue summons instead of a warrant of arrest. (Sec. 8(b), Rule 112)

Case: 

It bears stressing that it is within the discretion of the Judge to issue a warrant for the arrest of an accused in a criminal case. A Judge is required to personally evaluate the resolution of the prosecutor and its supporting evidence. He may immediately dismiss the case if the evidence on record clearly fails to establish probable cause. However, if he finds probable cause, then he is mandated by law to issue such warrant. While before, it was mandatory for the investigating Judge to issue a warrant for the arrest of the accused if he found probable cause, the rule now is that the investigating Judges power to order the arrest of the accused is limited to instances in which there is a necessity for placing him in custody in order not to frustrate the ends of justice. The arrest of the accused can be ordered only in the event that the prosecutor files the case and the Judge of the Regional Trial Court finds probable cause for the issuance of the warrant of arrest.(Pangan vs. Ganay, A.M. No. RTJ-04-1887. December 9, 2004)