Surprise witnesses will not be prevented from testifying in the impeachment trial of Vice President Sara Duterte as long as the contending parties provide at least a three-day notice before presenting them in the Senate impeachment court, Senate Secretary Renato Bantug said Monday.

Bantug, who serves as the impeachment court clerk, explained that since the procedure is “allowed in the rules of court,” the Senate would also adopt it.

“Both parties have the right to make reservations as to witnesses who may not be available yet during pre-trial,” he told reporters on the sidelines of day two of the pre-trial conference.

Both the prosecution and the defense, however, are required to notify one another at least three days before the scheduled appearance, Bantug added.

The defense and the prosecution are mandated to disclose their potential witnesses during the pre-trial conference — a closed-door meeting ahead of the trial proper — to streamline the proceedings.

Despite this, the parties are not discouraged from adding last-minute witnesses, provided that advance notice is given to avoid a so-called trial by ambush and to ensure fairness in the proceedings.

Surprise witnesses appearing in an impeachment trial is not unheard of.

To recall, the House prosecution in 2000 presented a surprise star witness — Clarissa Ocampo — who testified against then President Joseph Estrada at his impeachment trial, before the proceedings were aborted in January 2001.

Ocampo, a senior vice president at Equitable PCI Bank, linked Estrada to ill-gotten wealth and told the impeachment court that she personally witnessed him signing bank documents under the alias “Jose Velarde” in Malacañang to conceal a multibillion-dollar account.

Her testimony was a major turning point that triggered the EDSA 2 revolt that forced Estrada to step down on 20 January 2001.

In Duterte’s impeachment trial, the House prosecutors have ruled out presenting surprise witnesses, although earlier they disclosed, they had at least 57 witnesses who would potentially testify once the trial begins on 6 July.

The prosecution and the defense continued their pre-trial conference on Monday and hope to finish the marking of evidence, among other tasks, to advance the proceedings and allow the drafting of the pre-trial order for submission to the impeachment court.