In advance of the letter's release, One in Four, a victims' rights group, said that it wants Benedict to say "clearly and unequivocally" that the church "at the highest levels" has always known about abuse cases.
In its version of the letter, One in Four said it wanted Benedict to say the church had pursued a "deliberate policy of cover-up, protecting sex offenders in order to avoid scandal, with no regard for the safety of children" and that the scandal went beyond just the Irish church.
Greg Watts, the author of a biography of Pope Benedict XIV, said he expected more cases of abuse to surface in the future.
"What's happened in Ireland has happened in many countries," he told Al Jazeera on Saturday.
"I think there will be more revelations to come out form Poland and elsewhere because this type of thing is not unique to a particular country or culture.
"But I am dismayed by the church's inability to deal with this ... What we really need is reform of the government of the church. I think a lot of these problems that we've had is down to a secrecy among the bishops."
Predominantly Catholic Ireland has been shocked by three judicial reports in the last five years revealing ill-treatment, abuse and cruelty by clerics and a cover-up of their activities by church authorities.
In the last week, Cardinal Sean Brady, Ireland's top churchman, has come under fire after it emerged he swore two children to secrecy during a 1975 probe into their abuse by one priest, Father Brendan Smyth.
The allegations of abuse and cover-ups by church authorities go further and include allegations of abuses committed under Benedict's watch when he was Archbishop Joseph Ratzinger of Munich.
As leader of the Congregation for the Doctrine of the Faith, Ratzinger was responsible for a 2001 Vatican edict that instructed bishops to report all cases of child abuse to Vatican authorities in secret and made no mention of reporting crimes to the police.
"Is it not time for Pope Benedict XVI himself to acknowledge his share of responsibility?" said the Reverend Hans Kung, a Swiss dissident Catholic theologian.
The Netherlands: 200 cases of sexual abuse being investigated
Switzerland: 60 cases being investigated
Germany: 300 reported cases of sexual abuse
"Honesty demands that Joseph Ratzinger himself, the man who for decades has been principally responsible for the worldwide cover-up, at last pronounce his own mea culpa."
Benedict, who served as archbishop of Munich from 1977 to 1982, has yet to speak about the hundreds of abuse cases emerging since January in Germany.
These include the Reverend Peter Hullermann, who was already suspected of abusing boys in the western German city of Essen when Ratzinger approved his transfer to Munich for treatment in 1980.
There, Hullermann was allowed contact with children almost immediately after his therapy began.
He was again accused of molesting boys and was convicted in 1986 of sexual abuse.
He was suspended this week for ignoring a 2008 church order not to work with youths.