Sean Cardinal O’Malley, facing accusations of ignoring a priest’s letter that warned him three years ago about an allegedly predatory fellow cardinal, yesterday issued a statement saying it was an oversight by his secretary.

Ex-Cardinal Theodore McCarrick, 88, was stripped of his title in June after the Vatican found sex abuse allegations against him to be credible.

“In June of 2015 Rev. Boniface Ramsey sent a letter that was received at my office at the Archdiocese of Boston’s Pastoral Center. Rev. Robert Kickham, my Priest Secretary, received the letter on my behalf, as he does much of the correspondence that comes to my office at the Pastoral Center,” O’Malley wrote in a statement released by the Archdiocese of Boston yesterday.

“Fr. Ramsey’s letter came to me in my role as President of the Pontifical Commission for the Protection of Minors; specifically the letter presented matters concerning Archbishop McCarrick’s behavior with seminarians,” O’Malley continued. “Fr. Kickham’s response to Fr. Ramsey noted that individual cases such as he proposed for review fell outside the mandate of the Commission. Consequently, he did not bring the letter to my attention. In retrospect it is now clear to Fr. Kickham and to me that I should have seen that letter precisely because it made assertions about the behavior of an Archbishop in the Church. I take responsibility for the procedures followed in my office and I also am prepared to modify those procedures in light of this experience.”

Pope Francis ordered McCarrick, the retired archbishop of Washington, D.C., removed from public ministry June 20 after a church panel determined that allegations he sexually abused a teenager in New York more than 40 years ago were “credible and substantiated.”

The former altar boy alleged that McCarrick, then a priest, fondled him during preparations for Christmas Mass at St. Patrick’s Cathedral in 1971 and 1972. Since then, another accuser has said McCarrick first exposed himself to him when he was 11 and then engaged in a sexually abusive relationship with him for the next 20 years. McCarrick has denied the initial accusation but has not responded to the second one.

When McCarrick was removed, the New Jersey archdioceses of Newark and Metuchen revealed that they had received three complaints from adults alleging misconduct and harassment by McCarrick and had settled two of them.

O’Malley stated yesterday, “My first knowledge of Fr. Ramsey’s letter occurred when media reports of the letter were published last month. I apologize to Fr. Ramsey for not having responded to him in an appropriate way and appreciate the effort that he undertook in seeking to bring his concerns about Archbishop McCarrick’s behavior to my attention.

“Allegations regarding Archbishop McCarrick’s sexual crimes were unknown to me until the recent media reports,” O’Malley wrote. “I understand not everyone will accept this answer given the way the Church has eroded the trust of our people. My hope is that we can repair the trust and faith of all Catholics and the wider community by virtue of our actions and accountability in how we respond to this crisis.”

O’Malley also said the church hierarchy in the United States will be investigating how McCarrick was ever promoted in the first place.

“What makes all this so difficult to understand is that it has been my experience that when a priest is being vetted to be named a bishop, any doubt or question concerning his faithfulness to his promise of celibacy would result in removing his name from consideration to be named Bishop,” O’Malley wrote. “The Bishops Conference is anxious to understand how Theodore McCarrick could have been named Bishop, Archbishop and Cardinal. We must be certain that this never happens again. That is why the Bishops Conference are requesting an investigation by the Holy See with the participation of lay people.”

Herald wire services contributed to this report.