The Office of the Senate Sergeant at Arms (OSAA) has served a subpoena on Davao City Mayor Sebastian “Baste” Duterte, requiring him to testify in the ongoing impeachment trial of his sister, Vice President Sara Duterte.

The Senate impeachment court has scheduled Mayor Duterte’s appearance from September 28 to 30 after earlier setting his testimony for September 23. The schedule was adjusted to make way for oral arguments on the disputed voting threshold for conviction.

The House prosecution panel intends to present Mayor Duterte as a witness in connection with the Davao City government’s transactions with GenCorp Industries Inc., a company linked by prosecutors to the Vice President.

According to PhilGEPS Division Chief Rendell Sopeña’s testimony, GenCorp was awarded government contracts involving Davao City and other agencies. The Davao City government has said its transactions with GenCorp totaled more than ₱33.2 million across 19 contracts.

The prosecution has said Mayor Duterte may provide information on the city government’s transactions with GenCorp as part of its presentation under Article II of the impeachment complaint. The prosecution also intends to seek hostile-witness treatment, subject to the ruling of the impeachment court.

Mayor Duterte, however, said he and other Davao City government officials were unaware of Vice President Duterte’s alleged interest in GenCorp.

He also said the Vice President’s name does not appear in the company documents submitted for the 19 transactions.