MANILA - A Davao City councilor being linked to corruption in the Bureau of Customs was a no-show at the Senate hearing on the shipment of illegal drugs from China on Tuesday.

The Senate's Blue Ribbon Committee earlier has asked Councilor Small Abellera to attend the hearing upon the request of Senator Antonio Trillanes IV to verify the existence of the so-called "Davao Group."

• READ: Trillanes targets 'Davao Group' in shabu shipment probe

But Abellera skipped the investigation due to medical reasons, Senator Richard Gordon, chair of the committee, said.

"As usual, when somebody is called to the Senate, they always have an acute hypertension and the doctors would always advise," he said after Trillanes asked for an update on Abellera's supposed attendance.

The "Davao Group" floated in a previous Senate hearing when private broker Mark Taguba was asked to name personalities involved in bribery activities at the bureau.

The group supposedly dropped the name of presidential son, Davao City Vice Mayor Paolo Duterte, when transacting.

• READ: Palace: Show evidence of Paolo Duterte's wrongdoing

In a statement released the following day, President Rodrigo Duterte's eldest son said that Taguba himself admitted that the testimony against him was based on hearsay.

"Taguba admitted that his testimony against me was based entirely on rumors. Why would we entertain or believe a hearsay? One does not dignify lies with a response," he said.

Trillanes said in a previous interview with ANC's Early Edition that he wanted Abellera to attend the Senate hearing after Taguba and Customs Deputy Commissioner Gerardo Gambala, a former classmate of the lawmaker, claimed the existence of the Davao Group.

The senator said 5 informants "working within Customs and those within the proximity of Customs operations" confirmed that "they’re well-aware of the Davao Group."

"The question is, why would a councilor from Davao City be dealing with some brokers? This Small Abellera is known in Davao City to be very close to Paolo Duterte," Trillanes said.

Abellera's attendance, he added, would be helpful “so that we can trace and we can also test the credibility of Mr. Taguba.”

The Senate and the House of Representatives are separately investigating the shipment, which contained 600 kilograms of methamphetamine (shabu).

It supposedly slipped past Customs' green lane, which has relatively relaxed security checks compared to the red and yellow lanes, last May. Authorities eventually found the drug shipment in a warehouse in Valenzuela City.