Prabhunath Singh, his brother Dinanath Singh and Ritesh Singh were convicted in the case by the Additional District and Sessions Judge of Hazaribagh District Court.
Ashok Singh was elected from Mashrak assembly constituency in Bihar in 1995. He was killed 90 days after winning the poll in which he had defeated Prabhunath Singh.
Prabhunath Singh was in Janata Dal in 1995 and later joined Janata Dal-United (JD-U). At presently, he is with the Rashtriya Janata Dal (RJD). He is a strongman of Maharajganj Lok Sabha constituency of Bihar.
"My brother had defeated Prabhubath Singh in 1995. Prabhunath had openly said that my brother will be killed within 90 days of becoming legislator and was killed on the 90th day," Tarkeshwar Singh, Ashok Singh's brother, told a news channel.
The court would pronounce the sentence on May 23.
The case was transferred to Hazaribagh in Jharkhand from Bihar on the instruction of the Supreme Copurt.
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)