(Under the Revised Penal Code of the Philippines – Book One)

Article 16 of the Revised Penal Code identifies persons criminally liable as:

Principals
- Defined as the persons who directly participate in the execution of the crime.
- Modes of participation:
  a. By direct participation – They take direct part in the execution of the crime. Example: The person who fires the gun in a murder case.
  b. By inducement – They directly induce others to commit the crime. Example: A person offering money to someone to kill a rival.
  c. By indispensable cooperation – Their participation is indispensable to the commission of the crime. Example: A lookout who prevents the victim from escaping during a robbery.
Accomplices
- Defined as those who cooperate in the execution of the offense by prior or simultaneous acts, but whose cooperation is not indispensable.
- Example: A person who provides the tools for a burglary but does not participate directly in the crime.
Accessories
- Defined as those who participate subsequent to the commission of the crime, such as:
  a. Harboring, concealing, or assisting the principal or accomplice to escape.
  b. Destroying evidence of the crime.
  c. Profiting from the effects of the crime.
- Exceptions: Close relatives (e.g., spouse, ascendants, descendants, legitimate, natural, or adopted siblings) are not criminally liable as accessories, except when:
  - The crime is treason, parricide, murder, or infanticide.
  - The accessory profits from the crime.

The degree of participation affects the criminal liability of an offender. The Revised Penal Code recognizes three classifications of participation:

Principal
- Highest degree of participation.
- Penalties: They are subject to the full penalty prescribed by law for the crime.
- Liability: They bear the full responsibility for the offense due to their direct or significant participation.
Accomplice
- Lesser degree of participation compared to a principal.
- Penalties: One degree lower than the penalty for the principal.
- Liability: Limited to acts performed, showing a lesser degree of criminal intent or participation.
Accessory
- Lowest degree of participation.
- Penalties: Two degrees lower than the penalty for the principal.
- Liability: Restricted to their role in assisting the principal or accomplice after the commission of the crime.

Conspiracy (Art. 8)
- When two or more persons agree to commit a felony and decide to execute it, they are equally liable as principals, regardless of the specific acts performed.
- Requisites:
  a. A common design to commit the offense.
  b. Participation in the execution of the plan.
Complex Crimes (Art. 48)
- When a single act constitutes two or more grave or less grave felonies, or when an offense is a necessary means for committing another, the offender is penalized for the more serious crime and imposed the maximum penalty.
Collective or Individual Criminal Liability
- Individual responsibility: Based on the specific acts of participation.
- Collective responsibility: When conspiracy is proven, all conspirators are liable for the entire offense.
Mitigating, Aggravating, and Exempting Circumstances
- Affect the degree of participation and corresponding penalties.
- Examples:
  - Mitigating: Minor participation, lack of intention to cause a grave wrong.
  - Aggravating: Abuse of public position, evident premeditation.
  - Exempting: Insanity, minority.

Proportionality of Liability
- Penalties are assigned based on the degree of participation.
- Principals receive the full penalty.
- Accomplices and accessories receive reduced penalties in accordance with Articles 50-57 of the Revised Penal Code.
Special Circumstances
- Crimes involving public officials (e.g., malversation, graft) carry specific provisions for liability.
Prosecution’s Burden
- To establish the degree of participation, the prosecution must prove the extent of the offender's acts and intent beyond reasonable doubt.

Multiple Offenders (Habitual Delinquency)
- If the offender has been convicted multiple times within a specific period for crimes of similar nature (e.g., theft, estafa), they may face additional penalties under the Habitual Delinquency Law.
Collective Liability in Certain Crimes
- Complex Crimes: Liability is shared when one crime is used as a necessary means for committing another (Art. 48).
- Special Laws: Certain statutes (e.g., Anti-Terrorism Act) assign liability in broader terms, covering conspirators and indirect participants.
Plea Bargaining
- The level of participation may also determine the terms of plea bargaining, where a lesser charge may be negotiated based on the role of the accused.

People v. Medina (G.R. No. 123215)
- Clarified that mere presence at the scene of the crime does not constitute criminal liability unless it is proven that the person actively participated or conspired.
People v. Lizada (G.R. No. 170043)
- Explained that accomplices are liable only for acts within the scope of their cooperation, not for actions beyond what they facilitated.
People v. Llaguno (G.R. No. 128296)
- Highlighted that accessories are liable only when their post-crime actions meet the criteria of Art. 19.

This detailed breakdown ensures a comprehensive understanding of persons criminally liable and their degree of participation under Philippine law.