Grace called inmate-release procedures a "multilayer process that is complex" and involves a number of departments, including the county's Office of Judicial Support and the company that operates the prison.
"The human errors which are occurring are unacceptable," Grace said.
Grace said she knew of three prisoners' being mistakenly released this year and added that she was surprised to learn that media reports had documented as many as five. Grace also said she did not know that, according to a report on the state Department of Corrections website, two prisoners walked away last year.
The District Attorney's Office said Thursday bench warrants had been issued for Ateia Polk, 32, of the 4500 block of North 11th Street, and David Jeffrey Wilson, 19, of West 22d Street in Chester. Both were freed because of paperwork errors.
On June 14, murder suspect Taaqi "Fame" Brown of Germantown was released after he was confused with another inmate with a similar name. He turned himself in a day later.
Community Education Centers Inc. (CEC) of West Caldwell, N.J., has operated the country prison since January 2009. Officially known as the George W. Hill Correctional Facility, the Thornbury Township prison operates on a budget of $44 million from the county and houses about 1,800 inmates. It is the only privately run county prison in the state.
Calls Friday to John J. Clancy, chief executive officer of CEC, for comment were not returned. Prison Superintendent John A. Reilly and Warden Frank Green also did not return calls; nor did John Hosier, chairman of the board of the Delaware County Board of Prison Inspectors, and County Solicitor Robert DiOrio.
The District Attorney's Office said Friday that its criminal investigation division would also investigate the mistaken releases.
Susan Bensinger, a spokeswoman for the Department of Corrections, said county prisons "set and follow their own policies and procedures."
The state inspects prisons regularly. Delaware County passed its most recent inspection, in 2008. It is scheduled for another by the end of the year.
Contact staff writer Mari A. Schaefer at 610-892-9149 or email@example.com.