Additional district judge Omprakash Rai also acquitted two others due to lack of evidence.
Out of the 13, one person is absconding.
The case dates back to July 8, 1997 when Jagdish Sharma, a farmer of Devra Ahar village under Ghoshi police station, was shot dead in his field.
The deceased's brother Ram Kumar Sharma had lodged an FIR in the case against 15 persons.