The International Criminal Court ruled Friday that some testimony against Kenyan Deputy President William Ruto and a co-defendant, who are on trial for alleged war crimes related to post-election violence, was inadmissible.
The judges said prosecutors could no longer use depositions made before the start of the case by five witnesses who later recanted their testimony against Ruto and broadcaster Joshua Sang.
Ruto's lawyers were expected to renew their argument that the case should be dropped because of a lack of evidence.
Prosecutors said they were "currently studying" the decision. They have alleged that the witnesses who recanted their testimony were bribed or threatened to pull out of the case.
A similar case at the ICC against Kenyan President Uhuru Kenyatta collapsed last year, also after witnesses recanted their testimony.
The Ruto-Sang trial opened in 2013. Both men deny accusations that they provoked violence that left more than 1,200 people dead after Kenya's 2007 disputed elections.
Kenya's government has strongly criticized the International Criminal Court, which is based in The Hague, and has urged African countries to pull out of it, saying it unfairly targets African countries.
The Kenyatta case was a major test for the ICC, which has secured only two convictions since it began operating in 2002.
In 2014, Kenyatta became the first sitting president to appear before the ICC, when he attended a key hearing meant to determine whether the case against him should be dropped.
Had the trial gone forward, Kenyatta would have become the first sitting head of state to undergo prosecution at the ICC.