Impeaching a witness by prior conviction, or how valuable are Colanggo, et. al.’s testimonies in a court of law?

In the middle of the ongoing congressional investigation on the alleged illegal drugs trade in the New Bilibid Prison (NBP), a parade of convicts animatedly testified on the supposed involvement of several top-ranked government officials, including a seating senator of the land.

But what is the probative value of such testimonies as evidence?

In Section 11, Rule 132 of the Rules of Court lies the answer:

“Section 11. Impeachment of adverse party's witness. — A witness may be impeached by the party against whom he was called, by contradictory evidence, by evidence that his general reputation for truth, honestly, or integrity is bad, or by evidence that he has made at other times statements inconsistent with his present, testimony, but not by evidence of particular wrongful acts, except that it may be shown by the examination of the witness, or the record of the judgment, that he has been convicted of an offense.”

The Supreme Court, in the case of People of the Philippines vs. Francisco Nanas, alias Ikot (G.R. No. 137299, 21 August 2001), explains said Rule, thus:

“It is true that under the Rules of Court, a witness may be impeached by evidence that his general reputation for truth, honesty, or integrity is bad. However, a witness cannot be impeached by evidence of particular wrongful acts unless there is a showing of previous conviction by final judgment, such that not even the existence of a pending information may be shown to impeach him. In the present case, there was no testimony that the reputation of Beatisola for truth, honesty or integrity is bad. The defense merely presented evidence of the witness’ alleged previous wrongful acts by the introduction into evidence of criminal complaints filed by police officers and offended parties against the witness before the municipal trial court. There is no showing that these cases were eventually tried and that Beatisola was convicted thereof.”