The identity of the alleged assassin mentioned by Vice President Sara Duterte is not essential to proving the impeachment charge of grave threats, private prosecutor Atty. Armando Virgil Ligutan said on Thursday.

"No matter the finding of the NBI as to the identity of that assassin, that's irrelevant. The fact is she contracted an assassin," Ligutan told reporters.

He argued that Duterte's statements constitute what lawyers call an "admission against interest," saying the Vice President never denied making the remarks and instead reaffirmed them.

"We have what we call an admission against interest, an extrajudicial admission. If a person says something that would ordinarily expose her to criminal liability and still says it, it means it's true," Ligutan said.

He added that the issue is no longer whether Duterte spoke to someone about the alleged threat, but who that person is.

During Wednesday's impeachment proceedings, National Bureau of Investigation Director Melvin Matibag testified that investigators are still trying to identify the alleged assassin, saying the agency has narrowed its list to about 20 persons of interest.

Matibag declined to disclose their identities, citing the confidentiality of the ongoing investigation and the need to protect informants.

Ligutan also distinguished criminal prosecution from impeachment, saying the latter has a lower threshold because it deals with constitutional grounds such as betrayal of public trust.

"The question is whether it is enough to remove a public official. My goodness, yes," he said. "If we reach the threshold for a crime, then there is even more reason for that person to be removed from office."

The prosecution completed the presentation of evidence for Article IV, which covers the allegation of grave threats, on Wednesday.

The Senate impeachment court will resume proceedings on 29 July with the presentation of evidence for Article I, which concerns the alleged misuse of confidential funds. Hearings will also shift from 3 p.m. to 10 a.m. as the Senate resumes regular legislative sessions.