On Wednesday, just over two weeks after he admitted sheltering alleged molester priests, the bishop resigned in disgrace following his arrest in a fatal hit-and-run accident.
"I love and support the Catholic people, even those who may have felt disappointed in my leadership this past year," O'Brien said in a written statement.
The Vatican accepted O'Brien's resignation and appointed Santa Fe, N.M., Archbishop Michael Sheehan as interim administrator of the diocese in addition to his regular duties. In the early 1990s, Sheehan was sent to Santa Fe to clean up a wave of sex abuse scandals there.
The tragedy reaches beyond the hit-and-run victim's family and the Phoenix Diocese to the nation's Catholic bishops as they struggle to recover from the abuse scandal that has dragged on for 18 months.
Already this week, the leader of a bishop-appointed panel monitoring the abuse crisis has quit, putting renewed attention on the problem just as the prelates start their midyear meeting Thursday in St. Louis. Former Oklahoma Gov. Frank Keating stepped down from the National Review after comparing the secretive ways of some bishops to the Mafia.
"There is an accumulated sense among many people, maybe among many Catholics, that the bishops simply have lost control of the situation in some way," said Margaret O'Brien Steinfels, former editor of the Catholic magazine Commonweal.
O'Brien's case "is symbolic of that," she said.
For critics, the Phoenix bishop had already come to represent the hypocrisy of church leaders in the molestation crisis because of the deal he struck with a prosecutor to avoid indictment.
O'Brien admitted in the agreement announced June 2 that he protected abusive clergy. But as soon as the deal was made public, he gave interviews denying he covered up for anyone, prompting an angry response from Maricopa County Attorney Rick Romley.
Some Catholics also accused O'Brien of saving himself at the church's expense. As part of the deal, he relinquished some authority over the diocese. Church defenders were outraged that pressure from a civil authority had influenced how a diocese operates.
When O'Brien was arrested in a weekend hit-and-run, the Survivors Network of Those Abused by Priests made an immediate link with the abuse crisis. "He once again ignored the victim and drove away," said Paul Pfaffenberger, of the group's Phoenix chapter.
O'Brien, 67, was charged with leaving the scene of a fatal accident after a witness provided a license plate number and police traced it to the bishop's car. Investigators found the windshield caved in.
A pedestrian, Jim Reed, was killed. Reed, who was 6 feet tall and weighed at least 235 pounds, was jaywalking across the street when he was hit, authorities said.
The bishop told police he thought he had struck a dog or a cat or that someone had thrown a rock at his vehicle. He didn't report the accident, but prosecutors say he attempted to have his windshield fixed.
O'Brien told authorities he had a small amount of sacramental wine in a church service before the accident, but there was no indication that he was impaired, Romley said. The bishop could be sentenced to anything from probation to less than four years in prison if convicted.
"My heart is aching but I felt I needed to step aside for you, the Catholic people, to allow the diocese to heal from what has been a painful time in our history," O'Brien said.
At a Wednesday afternoon news conference, Sheehan said, "I come to be a man of hope and healing" and expressed concern for Reed and his family.
O'Brien is the latest among several prelates who pledged to lead the church out of the abuse crisis but wound up stepping down instead.
In May 2002, Archbishop Rembert Weakland of Milwaukee resigned after news broke that the archdiocese had paid $450,000 to a man claiming Weakland tried to sexually assault him. Weakland admitted an "inappropriate relationship" but denied abuse.
Cardinal Bernard Law resigned as archbishop of Boston in December following a stream of revelations about how he failed to discipline abusive priests.
Like Law, O'Brien had some impressive achievements as bishop.
He was responsible for bringing Pope John Paul II to Arizona in 1987, and in February 1989, O'Brien invited Mother Teresa to Phoenix to see the plight of the area's homeless people. As a result of her visit, Mother Teresa opened a home in Phoenix run by the Missionaries of Charity.
But Francis Butler, president of the Washington-based Foundations and Donors Interested in Catholic Activities, said the past year has seriously damaged the Phoenix Diocese.
Thousands of donors did not give to the diocese's most recent capital campaign, even though the fund-raiser reached its goal, he said.
"It appears to me, at least measured by donations, that people have been expressing displeasure with the leadership," Butler said. "They don't want to see any more bad publicity."
William Donohue, president of the Catholic League, an anti-defamation group based in New York, said O'Brien's case underscored the fatal flaw in the bishops' strategy to heal the church.
Although the pope has sole authority to remove bishops, the American prelates should take some action to discipline leaders who have mishandled cases of molester priests, he said.
"They know who the bad guys are," Donohue said. "What have they done about them?"