Walker, 40, was killed in the early hours of Aug. 18 as he walked home from an overnight shift at the 22nd Police District in North Philadelphia. Rafael Jones, the 23-year-old man charged in the killing, was released from prison 10 days earlier. Jones, who served four years in prison on a gun charge, was supposed to be under electronic monitoring as a condition of his release, but the monitoring was never set up. Jones also remained free after he failed a drug screening - despite a judge's order that he be arrested after even one positive test result.  The suit alleges that Jones was allowed to remain on the streets due to an "unwritten policy" employed by the board to limit probation and parole arrests. It is a tactic that board employees say is employed to create the appearance that the recidivism rates for parole and probation offenders are lower than they actually are, according to the complaint.