Corbett - who, as state attorney general, had overseen the Sandusky investigation - said Pennsylvania was the last state to allow such testimony.
Under the new law, expert witnesses for the prosecution and the defense will be able to testify about victims' responses to assault and abuse in general, but not to a witness' credibility.
The law covers all crimes that require registration as a convicted sex offender, such as rape, sexual assault, involuntary deviate sexual intercourse, and child sex offenses.
James Carpenter, chief of the Philadelphia District Attorney's Family Violence and Sexual Assault Unit, said the law would let prosecutors more clearly show how most victims respond to sexual assault.
"Jurors think victims should be running out of the house half-naked and screaming," Carpenter said, "but research and experience shows that is not the case."
David Harris, a professor at the University of Pittsburgh School of Law, said such expert testimony can counter defense lawyers' efforts to undercut accusers' testimony - such as by asking why an alleged victim stayed in touch with an alleged abuser or kept quiet for years about the alleged crime.
"This could be a very significant tool for prosecution," Harris said. "It's definitely more useful to the prosecution, whether it is titled like that or not."
He also predicted the law would pose problems for defendants who cannot afford to pay an expert witness.
"Defense counsel are likely to find themselves in a situation where they go to a judge and say, 'We're going to be in a position of fighting with one hand tied behind our back,' " he said.
But the bill's chief sponsor, State Rep. Cherelle L. Parker (D., Philadelphia), said the law was balanced and added that it took the legislature six years to approve it.
"We did not start working on this issue when the eyes of the world turned to Pennsylvania because of the two high-profile trials," she said. "This issue was important to us then, and it is now addressed."
Even so, said Shawn Wagner, district attorney for Adams County in south-central Pennsylvania, the two high-profile trials provided a crucial push for the bill.
Both juries were out when the state House of Representatives, without debate, voted final passage of the expert-witness bill and sent it to Corbett.
Both trials ended the next day, June 22, with Sandusky's conviction on dozens of child sex-abuse charges, and Msgr. William J. Lynn's conviction on one count of child endangerment. The latter verdict was the first time in the nation that a Catholic Church supervisor was found criminally liable for child sex abuse by a priest.
"But for the case in Philadelphia and the case in Bellefonte," Wagner said at the signing ceremony, "we would not be here this afternoon."
Contact Inquirer staff writer Mike Macagnone at 610-613-8829 or firstname.lastname@example.org.
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