HARRISBURG, Pa. — Six homicides allegedly committed by five Pennsylvania parolees over the past two months, including the slayings of two children and a Pittsburgh police officer, have struck a chord in the ranks of law enforcement and the state's prisons agency.

Calling the crimes "horrendous," state Secretary of Corrections John Wetzel told The Associated Press on Wednesday his agency will review the parolees' history in prison and under parole supervision and try to determine if something should have been done differently.

"These five are just so shocking that I think it requires a response from everybody in the system," Wetzel said in an interview.

The slayings have prompted calls from county prosecutors and the state corrections officers' union for a review of Pennsylvania's parole practices, although the president of the corrections officers' union said Wednesday that an internal review isn't enough for a system in which parole has become too automatic.

The arrests come on the heels of the state overhauling the parole system, helping lower the state's prison population and ballooning the ranks of parolees. Rank-and-file parole agents, meanwhile, say they have been stripped of discretion in their ability to temporarily remove a potentially dangerous parolee from the street.

One of those changes means Wetzel's agency now oversees parole agents in addition to Pennsylvania's state prisons, although the ultimate decision to release someone on parole is typically up to the Pennsylvania Board of Probation and Parole. Last year, 6,526 people under parole supervision were arrested, or almost 16% of the more than 41,000 total, according to Department of Corrections data.

That included 93 for murder. Most, or 4,676, were for non-violent cases, it said. Running totals for this calendar year were not available Wednesday.

Keith L. Burley listens during his extradition hearing at the Mahoning County Courthouse in Youngstown, Ohio. Pete Sirianni / New Castle News via AP File

The first charges, on July 9, spurred Wetzel's decision to order a review, he said. That arrest was Keith Burley, a convicted murderer who got out of prison in March and is now charged with killing an 8-year-old boy in the western Pennsylvania city of New Castle.

Burley's arrest caught the attention of the state corrections officers' union and county prosecutors, who questioned why someone with such a violent history had been paroled.

In the ensuing days, four other parolees were charged in slayings, most with connections to domestic violence.

One was arrested in the June 29 beating death of his girlfriend's 2-year-old son in Baltimore. Another was charged in the May 23 strangling of the 49-year-old mother of his girlfriend in her Hershey home before he allegedly set fire to the house to cover up the crime. In Lancaster, another parolee was charged in the fatal stabbing of his sister and niece. In Pittsburgh, another was charged with fatally shooting an off-duty police officer.

The parole board has declined to discuss its decisions or release documents that show its evaluation, citing state law that the agency says make it private, confidential and privileged. It does not vote in public or maintain a public database, docket or list of its parole decisions.

Wetzel declined to second-guess the parole board's decision-making, saying he is not privy to their internal deliberations.

"But the question is, is there some test we can be doing, is there some indication, is there something in this case or in any of these cases that we knew or should have known that should have changed how we make decisions and creating that feedback loop to improve decision making," Wetzel said.

Everyone in the system makes discretionary decisions, Wetzel said, "and sometimes they go bad."

Larry Blackwell, president of the Pennsylvania State Corrections Officers Association, said Wetzel's agency already had a chance to study the system that it helped create and an independent review is now necessary.

"You can't have an organization that failed at something investigating it," Blackwell said.

Parole decisions, he said, have become "machinery," a process of checking boxes rather than considering an inmate's history of violence.

Burley pleaded guilty in two assault cases in prison, but received sentences that did not add to his prison stay. Wetzel said Burley had no incidents of misconduct in the seven years leading up to his release.