PHILADELPHIA — A troubled police officer’s son who accuses two Roman Catholic priests and a teacher of raping him during boyhood is set to testify at a Philadelphia trial this week — and have his startling claims challenged in court for the first time.

The young man, identified by the pseudonym Billy in a 2011 grand jury report, testified in a landmark priest-abuse case last year. Lawyers for the church official on trial never cross-examined him, but now the strategy has changed.