I don't know what the answer is exactly, but this campaign of killing candidates cries out for a hardball response. Maybe Uribe should ask the legislature for emergency powers to appoint office holders in any case where a candidate has been killed or compelled to withdraw by threats. Then make the appointees, or some anyway, military officers. IOW a soft variety of martial law.
It's sad, really. If Uribe wins this fight his only thanks will be to be pilloried a decade hence by the "human rights" crowd. Witness Fujimori in Peru. In that case softness and moral ambiguity has even emboldened the Shining Path to the point of creating a resurgence.
It has to be stopped. This madness is going to spread (already started) across Latin America and the world. We are in a war against international terrorism and we must win.