MANILA, Philippines - Former Justice Secretary Alberto Agra denied a report from  National Bureau of Investigation (NBI) counter terrorism unit chief Ric Diaz about an alleged attempt to bribe a key witness in the Maguindao massacre case during his term.

Agra said on Sunday he would have called for an in-depth investigation about the incident had he been notified.

Justice Secretary Leila de Lima previously said Agra should explain his failure to order an investigation into Diaz' claim that a certain retired PAF Colonel Juanito Mariano tried to convince a key witness, Kenny Dalandag to change his testimony regarding the November 23 Maguindanao massacre, in exchange for P10 million.

The carnage left 57 people dead, including 30 journalists.

Diaz said the attempted bribery happened last June 10 at his office in the NBI, and that he subsequently informed Agra about it.

Agra said he is ready to be investigated so that government prosecutors could take action against the guilty parties, if there are any.

"I am open to any probe in order to shed more light on this deplorable incident," Agra said.

Agra said he found out only last Friday that there was an NBI report about the incident, but clarified that it did not come from Diaz, but from a deputy director whose name he has to verify.

Agra said the NBI report was submitted not to the Department of Justice's (DoJ) office of the secretary, but only to the DOJ's Witness Protection Security and Benefits Program headed by senior state prosecutor Leo Dacera.

De Lima earlier said the prosecutors investigating the attempted bribery will decide whether to summon Agra or former NBI director Nestor Mantaring to shed light on the incident.

Mantaring is being questioned on the incident in the wake of Diaz' claim that Mariano first went to the office of Mantaring before seeing him.

Diaz added that two NBI agents from Mantarin office accompanied Mariano to his office.