The man's death this past weekend came days before the scheduled preliminary hearing Thursday for the Rev. Robert Brennan. His lawyer had met with him last Friday.
"He had really straightened out his life. He was motivated to pursue justice. This was his goal, so this was shocking to all of us," lawyer Marci Hamilton said. "He made it through college. He was battling demons all the way through."
Brennan, 75, was described as an alleged serial abuser in a 2005 grand jury report on priest abuse in the Roman Catholic Archdiocese of Philadelphia, but he was never charged until this year because of legal time limits.
Prosecutors must now decide whether the rape case can go forward without the accuser's trial testimony. Two other men have filed civil suits against Brennan, and could potentially offer supporting testimony.
Defense lawyer Trevan Borum said he did not know what the other evidence might be, but said "obviously the central part of their case would have been the accuser's testimony."
Brennan was freed on $50,000 bail last week. He was suspended by the church after the 2005 grand jury report, and had been living in Perryville, Md.
The new accuser contacted the archdiocese in January, under expanded time limits, and said Brennan had sexually abused him from age 11 to age 14 at a northeast Philadelphia church, its rectory and at a movie theater. Brennan was arrested last month by prosecutors who credited the archdiocese for immediately sending the complaint their way.
"I cannot say enough about the bravery this young man displayed in coming forward to bring these crimes to light," District Attorney Seth Williams said in a statement Thursday.
Brennan had been transferred to Resurrection of Our Lord parish despite complaints dating to at least 1990 - from school administrators, a parent and other adults - of improper wrestling, touching and other inappropriate behavior around boys.
"It's just a tragedy compounded on another tragedy if the criminal case falls apart because of this," said lawyer Jeff Anderson, Hamilton's co-counsel, who focuses on clergy abuse cases. "It's our view that there's a long trail of evidence and survivors, some of whom have come forward."