Cardinal Sean P. O’Malley says he takes “full responsibility” for the failure of an allegation of sexual abuse against then-Cardinal Theodore McCarrick from reaching his hands, and pledged to change procedures in his office to prevent something similar from happening again.

O’Malley was widely credited with cleaning up the Archdiocese of Boston after taking over for the discredited Cardinal Bernard Law in 2003, and was appointed by Pope Francis to head the Pontifical Commission for the Protection of Minors in 2014.

Recently, Father Boniface Ramsey of New York said he sent a letter to O’Malley’s office in Boston in June 2015 which gave details of McCarrick’s alleged abuse against seminarians in New Jersey. Ramsey said he was told his allegations didn’t fall under the purview of O’Malley’s office, and that the priest should forward it to the appropriate Vatican department.

RELATED: Abuse letter to Cardinal O’Malley was second priest sent officials about McCarrick

In a statement released on Monday, O’Malley said the letter was received by his secretary, Father Robert Kickham, and that he personally was never made aware of the allegations.

“Father 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. Father Kickham’s response to Father 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,” O’Malley explained.

“In retrospect, it is now clear to Father 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,” the cardinal continued.

Ramsey has told media outlets that he also informed the papal ambassador in the United States at the time, Colombian Archbishop Gabriel Montalvo, who died in 2006, of concerns about McCarrick’s conduct, as well as Cardinal Edward Egan of New York, who died in 2015.

O’Malley said he first heard of the allegations against McCarrick this year from media reports, adding that he understands “not everyone will accept this answer given the way the Church has eroded the trust of our people.”

“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,” the cardinal continued.

“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 is requesting an investigation by the Holy See with the participation of lay people,” O’Malley said.

The Boston cardinal’s statement came the same day as Francis issued a letter to the “People of God” about clerical sexual abuse, issued less than a week after a Pennsylvania grand jury detailed allegations of over 1,000 cases of abuse by 300 priests over the last 75 years in the state.

RELATED: Pope vows accountability for sex abuse cover-ups but offers no new specifics

Francis wrote Monday “no effort must be spared to create a culture able to prevent such situations from happening, but also to prevent the possibility of their being covered up and perpetuated.”

The sexual abuse crisis is threatening to overshadow the pontiff’s Aug. 25-26 visit to Ireland for the World Meeting of Families in Dublin.

O’Malley has cancelled his scheduled appearance at the event in order to investigate allegations of sexual misconduct at Boston’s St. John’s Seminary.