Prosecutors are preparing to argue for the conviction of a former death-row inmate at an upcoming retrial for a 1966 quadruple murder in central Japan, a source familiar with the matter said Saturday.

The move comes despite the prosecutors' decision not to appeal a high court order in March that granted a retrial to Iwao Hakamata, laying the ground for his exoneration. Hakamata, 87, spent nearly half a century behind bars before new evidence led to his release in 2014.

The prosecutors plan to convey their position on Monday to the Shizuoka District Court, where the case will be tried again, likely triggering a backlash from Hakamata's lawyers who have called for a swift conclusion of the trial and his acquittal.