All of the people affected had consumed the local beer, pombe, on 9 January, which had been inadvertently contaminated by the bacterium Burkholderia gladioli which produced the toxic compound bongkrekic acid.

[9][10] An alternative early theory, presented in Forbes magazine online, suggested the active ingredient in such poisonings was perhaps a cardiac glycoside, such as digitalis.

[6] Kroll cites Norman Z. Nyazema, a researcher into traditional practices and culture of Africa, who suggested that organophosphate pesticides may instead be to blame, though the cause of the deaths would remain a mystery until forensic testing was complete.

[8] The investigation into the cause of the poisoning eventually turned up the presence of the bacterium Burkholderia gladioli and two toxins which it produced, bongkrekic acid and toxoflavin, in both the beer and the corn flour that was used to help brew it, and concluded that these were responsible for the deaths and illnesses.

The investigative team determined that flood-damaged corn flour that had begun to rot had been offered to the brewer in the mistaken belief that, while unfit for use as food, it was still suitable for use in brewing.