MANILA - Senator Antonio Trillanes IV on Monday called for a Senate inquiry into President Rodrigo Duterte's alleged involvement in the killing of people in Davao City through the "Davao Death Squad" or DDS.

In a privilege speech, Trillanes presented his own investigation into the testimony of self-confessed hitman and "Davao Death Squad" member Edgar Matobato.

According to Trillanes, his research and fact-checking showed that there were no inconsistencies in the testimony of Matobato, contrary to claims of other senators, including Senator Alan Peter Cayetano.

• READ: Solons question Matobato 'tendency to change answer'

In his presentation, Trillanes presented evidence that Matobato was telling the truth about his identity and his job as a hitman.

The senator then asked his fellow lawmakers to look into Duterte's direct involvement in the killing of around a thousand persons during his term as mayor of Davao City.

"Now that we have seen the different corroborating evidence on the testimony of Mr. Matobato, we are faced with a very frightening prospect: that of having a mass murderer as president of the country," he said.

"All that has changed, we cannot look the other way anymore, because now, Edgar Matobato is staring us in the face. He has testified that President Duterte, as mayor of Davao City, was the mastermind behind the Davao Death Squad, which was responsible for the killing of more than a thousand persons from 1998 to 2013," Trillanes added.

Trillanes asked the Senate to refer his privilege speech to the Senate Blue Ribbon committee for a possible accountability probe into the former Davao City mayor.

He also called for a probe on other public officials involved in the activities of the DDS.

Matobato, who first appeared at the Senate inquiry on drug-related killings last September 15, linked Duterte to a string of killings from 1988 up to 2013.

• READ: What a self-confessed DDS hitman told the Senate