Attorneys for an inmate accused of murdering a federal correctional officer cited a Citizens’ Voice investigation into the case as they laid the groundwork Wednesday to spare him from the death penalty.

For a December story the paper obtained closely guarded prison documents that showed a stark shift in the way the inmate Jessie Con-ui was disciplined. Treatement ranged from a near zero-tolerance approach for minor offenses in 2008 to leniency shown in 2012. The change came as political leaders and civil liberties groups pressured the Bureau of Prisons to reduce the number of restricted-housing inmates and as the bureau started tying those reductions to bonuses for wardens and other high-ranking officials.

Now attorneys are demanding a federal investigation to determine the source of confidential material that aided The Voice’s reporting, including inmate Jessie Con-ui’s discipline and transfer records and a report on a psychological evaluation he submitted to less than 48 hours after the killing.