MANILA, Philippines -- The grievance of slain hostage-taker Rolando Mendoza ?- his dismissal from the Philippine National Police by the Ombudsman without ``due process'' ?- has been lost in the post-mortem of Monday's embarrassing hostage drama in Manila.

Inquiries by the Senate and the House of Representatives should also tackle the root cause of Mendoza's ``sense of injustice'' and summon the Ombudsman, Bayan Muna party-list Representative Neri Colmenares said on Sunday.

``The root cause of all this is the sense of injustice. He felt so aggrieved that he had to resort to hostage-taking,'' he said by phone. ``The key to the investigation is what drove him to commit this act. The key there is the Ombudsman.''

Colmenares, a member of the House committees on justice, human rights and suffrage, said both chambers of Congress should summon Ombudsman officials to explain the handling of Mendoza's case.

``Whatever the reason and whether he committed the act or not (extortion), we should ask the Ombudsman how it handled the case,'' he said.

Mendoza hijacked a tourist bus carrying 25 mostly Hong Kong nationals Monday morning in Manila, fatally shooting eight when negotiations bogged down before being killed by snipers.

The bemedalled police officer vented his frustrations on the Ombudsman which dismissed him on charges that he extorted from a civilian despite appeals to Ombudsman Merceditas Gutierrez.

In his interview with a local radio, Mendoza said that the Ombudsman dismissed him after hearing his case for seven months, but had not acted on his letters of appeal nine months after he submitted them to Gutierrez.

During the negotiations, he scoffed at Gutierrez's letter assuring that his case would be reviewed, branding it as trash and indicating that he expected one that either reversed or upheld his dismissal.

The Senate last week opened its inquiry into the crisis that embarrassed the country, and threatened diplomatic relations between Beijing and Hong Kong, and the Philippines.

The House, specifically the committee on public order, is set to mount its own inquiry into the drama that has exposed the police's lapses, media's excesses and the leadership's poor response.

Colmenares observed that the Ombudsman dealt with Mendoza more swiftly than it did with high-ranking police officials implicated in ``Euro generals scandal,'' and who were interrogated at the Moscow international airport for carrying an undeclared 105,000 euros or P6.9 million in en route to an Interpol conference in October 2008 .

``How come the dismissal has been swift? In contrast, it's taking them time to resolve the case of the Euro generals, which is an open and shut case, and which any law student can argue to convict the generals since the law is clear that you can't bring $10,000 out of the country,'' he said.

He said that a ``sense of injustice'' arose when higher ranking officials were treated as ``untouchables.''

Colmenares believed that a closure of the case would not be complete without the Ombudsman?s explanation on its actions on the case.

``To resolve the sense of injustice, it's crucial that the Senate and the House include the Ombudsman in the investigation. We should not pay lives for the error of the Ombudsman,'' he said.

House Majority Leader Neptali Gonzales II, however, said that nothing could justify Mendoza's action of taking civilians hostage.

``I can't side with him on this issue. Whatever his beef was, no one is above the law. We've seen some policemen separated from the service, and only a few had the propensity of causing a sense of national shame,'' he said by phone.

``Assuming that he was unjustly treated, the manner by which he took the law into his hands can never be justified,'' he added.

He said that the House inquiry should focus on the PNP's capability in handling conflict situations, and pinpoint those responsible for the grim outcome of the drama.

``There is no question that what resulted in the operation was a national embarrassment. I hope that's not an indication that the PNP is ill-prepared, ill-equipped in handling such a situation. Using a sledgehammer to smash the windows of the bus is too archaic. If this is the best that the PNP can offer, then we're in a lot of trouble,'' he said.