MANILA - A law dean believes the charges filed by the Ombudsman against former President Benigno Aquino III in relation to the Mamasapano carnage are light and weak.

Fr. Ranhilio Aquino, San Beda Law Dean, said the former president should be held liable not for usurpation of authority or graft, but for the death of the 44 Special Action Force (SAF) troopers.

"Kung sabihin mong kasalanan niya lang 'yung pinayagan niya si Purisima na magbigay ng orders... I think he has a more direct participation in the death of the SAF 44," he told DZMM Tuesday.

• READ: Aquino to face trial for Mamasapano carnage: Ombudsman

Also included in the charges were former national police chief, retired Director General Alan Purisima and the former chief of the police Special Action Force, retired Director Getulio Napeñas.

The law dean believes text messages between Aquino and Purisima bared during a Senate inquiry is incriminating evidence that would have been a basis for a stronger case.

Fr. Ranhi added that it is wrong for the Ombudsman to solely base her indictment on the results of the Senate and House inquiries as she is mandated to conduct a thorough investigation.

"Kung 'yan lang ang ikakaso sa kanya, that's a very light case. It would be good for the office of the Ombudsman to conduct a malalaliman, thorough and very transparent investigation," he said.

The camp of former President Aquino said they have already received the order from the Ombudsman and that they will be filing a motion for reconsideration on Tuesday.

"Former President Benigno Aquino III received the order of the Ombudsman this afternoon and is currently studying it with his lawyers, with the end view of filing a motion for reconsideration, said his former deputy spokesperson Abigail Valte.

In an exclusive interview with the Philippine Daily Inquirer, Aquino said he was caught by surprise by the filing of the complaint but added that "his conscience is clear."

Meanwhile, President Rodrigo Duterte earlier defended his predecessor from the Ombudsman's charges, saying it was a "silly" decision to charge Aquino with usurpation of authority.

Duterte said the former president's actions were justified since he was the commander-in-chief and had the full authority and discretion over any police or military operation.