(CNN) -- Monsignor William Lynn, the highest-ranking cleric accused of imperiling children by helping cover up sexual abuse, was found guilty Friday of one count of child endangerment.
He was found not guilty on a second count of endangerment and a conspiracy charge to protect a priest accused of abuse.
The jury was unable to bring a verdict against his co-defendant, the Rev. James Brennan, who was charged with attempted rape of a 14-year-old altar boy and endangering the welfare of a child.
Lynn was taken into custody after Friday's verdict, when the judge revoked his bail. His lawyer, Jeffrey Lindy, derided the decision not to let his client remain free on bond prior to sentencing, calling it "an unspeakable miscarriage of justice (for) a 61-year-old man with no prior record and long established ties to the community."
He is set to be sentenced August 13, court officials said, and could face up to seven years in prison for his conviction on a third-degree felony.
The trial marked the first time U.S. prosecutors charged not just priests who allegedly committed abuses but church leaders for failing to stop them.
Calling the verdict "historic," Philadelphia District attorney R. Seth Williams said Friday's decision sends a message about potential consequences of not reporting sexual abuse.
"Many people of many generations have unclean hands when it comes to this silence," Williams said, adding that others could also be investigated.
Terence McKiernan, who heads the advocacy website BishopAccountability.org, called the conviction "a watershed moment in the Catholic abuse crisis."
"Because of the Lynn verdict, bishops and church officials are now accountable. They are no longer immune from judgment and punishment," McKiernan said.
And Marci Hamilton, a victims' rights attorney, said the jury's verdict Friday -- as well as the decision by now-defrocked priest Edward Avery to plead guilty after admitting to sexually assaulting a 10-year-old altar boy -- suggests "the picture is now clear that the Philadelphia archdiocese permitted crimes against children."
The archdiocese issued its own statement after the verdict, though it did not mention the trial or either Lynn or Brennan by name. It did, however, insist that "the lessons of the last year have made our Church a more vigilant guardian of our people's safety."
"The Archdiocese of Philadelphia is on a journey of reform and renewal that requires honesty and hope," it said. "We are committed to providing support and assistance to parishioners as they and the Church seek to more deeply understand sexual violence, and to create an environment that is safe and welcoming to all, including past victims."
Lynn's attorney said he felt the jury agreed there was no "far flung conspiracy," though he conceded the prosecution "scored a victory" in securing the lone conviction -- one that made he and the monsignor "extremely upset."
"By finding him guilty, they're saying he helped endanger children," Lindy said. "It's the last thing he wanted to do. ... I don't think he's the evil person the district attorney is making him out to be."
Bill Donahue of the Catholic League, an advocacy group devoted to challenging defamation of or discrimination against Catholics, called the verdict a defeat for overzealous prosecutors and victims advocates who he claimed had unfairly targeted church leaders.
"The witch hunt has come to an end, and those who have been clamoring for blood lost big time," Donahue said in a statement. "They wanted the big prize -- they wanted to nail a high-ranking clergyman on conspiracy. ... Looks like their car ran out of gas in Philadelphia."
More than 60 witnesses and alleged clergy abuse victims testified during Lynn and Brennan's criminal trial, which began March 26 and wrapped up May 31, with jury deliberations beginning the next day.
Lynn's defense team argued that their client repeatedly told higher-ups about the alleged abuse and, under strict orders from late Cardinal Anthony Bevilacqua, had no authority to remove priests from the ministry.
Assistant District Attorney Patrick Blessington characterized Lynn's behavior as "disgraceful," "shameful" and "ridiculous," sarcastically calling him a "hero" who put young people in harm's way.
"He actually looked you in the eye and said he put victims first. How dare he?" the prosecutor asked jurors during his more than 2½-hour closing argument.
Lynn's conspiracy count related to an allegation that he schemed with Avery and other archdiocese officials to endanger children.
Avery had been due to go on trial with Brennan and Lynn, but he pleaded guilty in March to a sexual assault that occurred during the 1998-99 school year.
The 69-year-old was sentenced to 2½ to five years in prison.
Brennan himself was removed from the active ministry in 2006. Two years later, he admitted that he had allowed the youngster to view pornography and sleep in the same bed with him in 1996, according to church investigators' testimony.
CNN's Ross Levitt contributed to this report.