Bruce Castor Jr.

HARRISBURG — The former county prosecutor taking over for Pennsylvania’s convicted attorney general is a central figure in the Bill Cosby case, having chosen a decade ago not to charge the entertainer with sex assault and then saying the decision was binding when called to the witness stand this year by Cosby’s lawyers.

Bruce Castor Jr., 54, took the oath privately Wednesday as the state’s top law enforcement official, an office spokesman said.

He succeeds Kathleen Kane, a Democrat who resigned following her conviction on charges she abused the powers of her office by leaking secret grand jury information to smear a rival and then lied under oath to cover it up. Castor will serve out the five months left of Kane’s term.

Castor, a Republican, served two terms as the district attorney in Montgomery County, in suburban Philadelphia, before becoming a county commissioner. He ran for attorney general in 2004, losing in an expensive and hotly contested party primary to Tom Corbett, who later went on to become governor.

Last fall, Castor made an unsuccessful bid to return as the county’s top prosecutor in a race in which he was criticized by his opponent for not pursuing charges against Cosby in 2005.

The district attorney-elect ended up filing a felony sex assault charge against Cosby, who has denied any wrongdoing.

Castor emerged as a key witness at a hearing in February at which Cosby’s lawyers tried to have the comedian’s case thrown out. He testified he had promised Cosby that Cosby would never be charged over a former Temple University employee’s allegation that he molested her at his suburban Philadelphia home in 2004. But a judge rejected his claim after prosecutors cited inconsistencies in Castor’s accounts and challenged his credibility.

Not long after that testimony, Kane tapped Castor as her second-in-command.

At a news conference Tuesday, Castor said he believed he was the right person to take over from Kane, following two years of turmoil in the office.