The court of Additional District Judge (ADJ) Nand Kumar Shrivastava said the quantum of punishment would be announced on next Wednesday.
Krishna, his son Chanakya Singh, his servant Gagan and bodyguard Umesh Singh have been found guilty of killing JD(U) leader and transporter Satyendra Singh in Patna in 2009.
Krishna and two others who were present in the court today were taken into custody after the verdict cancelling their bail.
His son Chanakya Singh is already lodged in the jail in the case.
At present, he is a General Secretary in RJD.