Nimbalkar was killed in June 2006 and former MP Padamsingh Patil is the key accused in the case.
Omprakash in his deposition told the court about the strained relationship between his father and Patil.
He also said that his father had filed a few police complaints Patil.
Omprakash told the court that his father was elected director of Terna Sugar Factory and later became director of Osmanabad District Central Co-operative Bank Ltd with the help of the accused.
More From This Section
He further said in 2002 the district bank invested Rs 30 crore in a firm named M/s Home Trade, but it the bank did not get the money back.
The trial began in July 2011.
According to the CBI, Patil hatched the conspiracy "to kill Nimbalkar out of political rivalry".
Other accused in the case include Laturbased businessman Satish Mandade, corporator Mohan Shukla, Parasmal Jain, former state excise inspector Shashikant Kulkarni, Bahujan Samaj Party worker Kailash Yadav and alleged shooters Dinesh Tiwari, Pintu Singh and Chote Pandey.