Jones' case also led state officials to acknowledge that under the state house-arrest program, prisoners are sometimes allowed to go without electronic monitoring for a time after their release.
In his statement, Corbett said he had ordered Michael C. Potteiger, chairman of the Board of Probation and Parole, to conduct the internal investigation "to determine if there were any policy failures or employee errors."
"I want to know the facts," Corbett said.
The board declined to comment, but last week it said it was reviewing its policies on monitoring probation offenders.
Also Thursday, State Sen. Mike Stack (D., Phila.) sent a request to the Judiciary Committee for a hearing on the events preceding Walker's death. Stack is a member of the committee. "The system designed to protect the men and women who protect us failed," Stack said in an e-mailed statement. "Officer Walker's family and colleagues deserve a prompt and full examination of what happened and reasonable assurance that it won't happen again."
State Rep. Brendan F. Boyle (D., Phila.) announced he would host a hearing with the House Democratic Policy Committee in Philadelphia next month on parole procedures. Members of the probation and parole board will be expected to testify, Boyle said.
"This type of lapse in procedure is absolutely unacceptable," Boyle said in an e-mailed statement. "My colleagues and I hope to find some answers about how this could have happened and ensure that the necessary steps are taken so that something like this never happens again."
Along with Jones, police have charged 19-year-old Chancier McFarland in Walker's slaying.
Police said Walker, a 19-year veteran of the force, was walking to a bus stop around 6 a.m. Aug. 18 after finishing his overnight shift at the 22d District in North Philadelphia. He was in street clothes, and surveillance video captured two men as they followed him. Police said that the men announced a robbery and that when Walker went for his gun, Jones shot him multiple times.
Jones has a criminal record dating back more than 10 years. After serving four years in prison on a gun charge, he was arrested in February on charges of robbery. The case fell apart when the witness failed to testify, but on July 25, Common Pleas Court Judge Susan I. Schulman ordered Jones put on house arrest for violating his probation. She also ordered weekly drug tests, with the stipulation that he would be arrested immediately if he failed one.
Two days after Jones left jail, he reported to the Board of Probation and Parole on Aug. 10 and tested positive for marijuana, according to documents obtained by The Inquirer. He reported again on Aug. 15, those records show.
A copy of the parole board's supervision history - its internal record of Jones' case from his release from prison in October 2011 to his arrest in Walker's killing - details his Aug. 10 visit to the parole board office and his failed drug test. Jones told a probation officer he had used marijuana while still in jail, and he was told to report to his probation officer the next week.
But the supervision history The Inquirer obtained makes no mention of the Aug. 15 visit, raising questions about the board's accounting of the case. Probation officer sign-in logs that The Inquirer reviewed list Jones as having signed in for his visit at 3:50 p.m. that day.
Three law enforcement sources have said Jones' parole officer, Jose Rodriguez, detailed for them how he had asked his supervisors for an arrest warrant for Jones on Aug. 15. Board officials have yet to explain why Jones was not arrested then, as mandated by the judge's order.
The circumstances call to mind the 2008 killing of Philadelphia Police Officer Patrick McDonald, who was shot by Daniel Giddings weeks after Giddings walked out of a halfway house.
The halfway house staff had been tasked with supervising the release of Giddings, a violent criminal who served 10 years in prison for a carjacking and who had amassed a record in prison that included stealing from cellmates, assault, and lengthy stays in solitary confinement. After failing twice to make parole, he was released to the halfway house in August 2008.
Giddings escaped from there a week later. The next month, he shot and killed McDonald.
In the days that followed, Gov. Ed Rendell ordered the Department of Corrections to suspend the release of all offenders recommended for parole, pending an independent, top-to-bottom review of the process. He also called for a full investigation into the decision to parole Giddings.
"We are looking at it to see if it was a bad judgment call," Rendell said at the time.
The parole freeze was lifted two months later, after a report found the state's procedures were "largely safe."
The Jones case also has illuminated the difference between the state and county probation systems. Last week, Potteiger said Jones was released without monitoring because there was no telephone line in the home where Jones was supposed to live, as required for electronic monitoring.
"The procedures of the board do not require a parole agent to escort an offender from prison to a parole office in order to have a radio frequency electronic monitoring device placed on the offender," his statement said.
In the county probationary system, the opposite is true. Defense attorneys regularly complain that their clients are not released on electronically monitored house arrest until the county probation officer has a bracelet available and the probationer's home has been inspected and the necessary landline installed.
As a result, some probationers remain in prison for weeks or months until one of the limited number of electronic devices becomes available.
In June, the shortage of electronic bracelets came up at the bail hearing of Msgr. William J. Lynn, the Archdiocese of Philadelphia official who was taken into custody June 22 after being found guilty of child endangerment in the church sex-abuse trial.
At a June 26 hearing, Common Pleas Court Judge M. Teresa Sarmina said she was inclined to release Lynn on bail pending sentencing if he were electronically monitored. Lynn's lawyers contended the 61-year-old cleric, convicted for his role in the cover-up of sexual abuse of minors by priests, would not be a threat to the community or a flight risk.
But after prosecutors said it could be months before a monitoring device was available, Sarmina ordered Lynn held without bail until he was sentenced on July 24.
Contact Allison Steele at 215-854-2641 or firstname.lastname@example.org.
Inquirer staff writer Joseph A. Slobodzian contributed to this article.