Section 4. Plea of guilty to non-capital offense; reception of evidence, 

Consequences of Plea of Guilty
   - As a rule, a plea of guilty is an unqualified admission of the
     crime and of the attending circumstances (aggravating and/or
     qualifying) alleged in the complaint. Such plea removes the
     necessity of presenting further evidence and for all intents and
     purposes the case is deemed tried on its merits and submitted for
     decision. However, the court may, upon motion, allow the
     presentation of evidence to prove aggravating and mitigating

     The trial court may allow an accused to plead guilty and at the
     same time allow him to prove other mitigating circumstances.
     However, if what the accused would prove is an exempting
     circumstance, which would amount to a withdrawal of his plea of
     not guilty.

     If the accused is permitted to present evidence after his plea
     of guilty to a non-capital offense and such shows that the
     accused is not guilty of the crime charged, the accused must be
     acquitted, for there is no rule which provides that simply because
     the accused pleaded guilty to the charge that his conviction
     automatically follows. Additional evidence independent of the
     plea may be considered to convince the judge that it was
     intelligently made.

     For non-capital offenses, the reception of evidence is merely
     discretionary on the part of the court. If the information or
     complaint is sufficient for the judge to render judgment on a
     non-capital offense, he may do so. But if the case involves a
     capital offense, the reception of evidence to prove the guilt
     and degree of culpability of the accused is mandatory.

Section 5. Withdrawal of improvident plea of guilty

Instances Of Improvident Plea:
1. Plea of guilty was compelled by violence or intimidation
2. Accused did not fully understand the meaning and consequences of
   his plea
3. Insufficient information to sustain conviction of the offense charged
4. Information does not charge an offense
5. Court has no jurisdiction

When Improvident Plea may be Withdrawn
   - At any time before judgment of conviction becomes final, the court
     may permit and improvident plea of guilty to be withdrawn and be
     substituted by a plea of not guilty.

People vs Lambino, 103 Phil 504 (1958)
   - The withdrawal of a plea of guilty is not a matter of right to the
     accused but of sound discretion to the trial court.

The reason for this is that trial has already begun and the withdrawal
of the plea will change the theory of the case and put all past
proceedings to waste. Moreover, at this point, there is a presumption
that the plea was made voluntarily.