Nairobi, Jan. 4 -- The modest setting of the Mombasa Magistrate's Court, where Yusuf Abubakar Joho is testifying as a prosecution witness, provides can't hint of the billions of shillings at stake-until the Mining Cabinet Secretary's brother begins to speak.

Mr Abubakar-popularly known as Abu-speaks with intensity about the long-running battle his family has fought with one of the most powerful men in Kenya. Mohammed Jaffer, a reclusive billionaire who styles himself as the "port man," has over the years entrenched his commercial dominance at the country's largest port, retaining an iron grip over critical import infrastructure.

Through the MJ Group, which he chairs, and his son Mujtaba operates, Jaffer has for years exercised dominant ...