Kenya is at a pivotal moment. After the devastating post-electoral violence a year ago, the country has an opportunity to investigate and prosecute those responsible before political tensions rise again in the run-up to new elections, probably in 2012.

Firm public leadership is needed by Kenya's unity government to overcome resistance from certain parliamentarians who, fearful of being held to account for their role in the violence, are ready to subject Kenyans to a new round of bloodshed.

The Waki Commission, established to examine the violence, rightfully saw the problem as one of impunity.

Certain officials, politicians and community leaders resorted to violence because they calculated that they could get away with it.

To end that impunity, the Waki Commission recommended establishing a special tribunal in Kenya to investigate and punish the orchestrators of the violence.

And to avoid the tribunal being infected by corruption and political interference that so often undermines Kenya's regular justice system, the commission recommended that extraordinary steps be taken to guarantee the tribunal's independence.

These include involving international jurists among the judges and prosecutors, establishing an independent budget and constitutional authority outside the regular justice system, drafting special rules on appointments and immunities, and encouraging the International Criminal Court in The Hague to play a back-stopping role should things go wrong.

But in February, the Kenyan parliament rejected a Bill to make the constitutional changes needed to secure the special tribunal's independence.

Certain ministers with the most to fear from vigorous, independent prosecutions said they preferred to delegate the matter to the International Criminal Court.

This was ostensibly because of the ICC's greater independence but, in reality, it was because they calculated that it was less likely to act quickly or effectively.

However, the debate in parliament was a red herring. The ICC is independent. Its decision to intervene will not depend on the Kenyan parliament; it can step in whenever the Kenyan government fails to deliver justice.

Knowing that, only those who fear the special tribunal would oppose it. Does Kenya's parliament really want to earn itself an international reputation as a promoter of impunity?

If properly instituted, there is no question that the proposed special tribunal would be superior to prosecution by the ICC.

The ICC, an international tribunal, would most likely hold trials in The Hague, while the special tribunal, a Kenyan institution, would hold trials within the country.

This would make the experience more meaningful for the Kenyan people, and would leave a legacy of experienced prosecutors and investigators to address political violence in the future.

The ICC would pursue, at most, the top officials involved in the violence; the special tribunal would prosecute a more comprehensive set of those responsible for the killings and other abuses.

The ICC tends to move slowly, with prosecutions taking years to unfold; the special tribunal would be quicker and nimbler, and could begin prosecutions well before electoral tensions flare again.

There may, ultimately, be a role for the ICC, but it should be a court of last resort, stepping in only if Kenya proves itself unable or unwilling to pursue justice itself, not the first port of call.

Unfortunately, the Bill for a special tribunal initially introduced by the government was poorly prepared, leading even some genuine proponents of justice to oppose it, and leading to its defeat.

The government can enlist the support of those who want justice, while isolating the opponents of fair prosecutions, through greater care in preparing a new Bill for submission to parliament.

First, the government, before submitting the Bill, should consult broadly not only with parliament but also with the civil society and the legal community, to identify perceived problems and take corrective measures.

In addition, the government should make it clear that it will not tolerate the spectacle of ministers or assistant ministers working against such an essential part of its programme, whether through their own votes or the votes of their followers.

Their personal interests in undermining the prospect of prosecution should not stand in the way of the nation's interest.

Finally, both President Mwai Kibaki and Prime Minister Raila Odinga should use their moral authority to send a strong public message that the perfect should not be the enemy of the good - that the special tribunal may not be ideal but that the choice between the special tribunal and the ICC is a false one.

There are only two choices: Justice or impunity.

In the first instance, the Kenyan government and people should bear primary responsibility for seeing justice done.

That is the best way of breaking the deadly cycle of violence and impunity in Kenya and deterring the devastation that would come from another round of political violence.

Kenneth Roth is executive director of Human Rights Watch