An undertrial prisoner accused in a murder case was gunned down by four criminals on the Saharsa civil court premises on Tuesday. One of the assailants, identified as Alok Kumar, son of Bhupendra Yadav of Pushpalan Colony, was caught with a country-made pistol and a live cartridge. The police recovered five empty shells from the spot. Prabhakar Kumar (20) was shot soon after he stepped out of the court room following the hearing in his case.