Amid mounting criticism over the presence of such cardinals, notably Roger Mahony of Los Angeles, among the men who will choose a successor to Pope Benedict XVI, Monsignor Charles Scicluna said they had kept quiet "out of fear of scandal."
Citing canon law, he said the cardinals "have the right and duty" to vote in the conclave.
"Wisdom is not [God]-given just to saints but also to sinners," said Scicluna, who was in charge of Vatican efforts to combat the scourge of predator priests before his promotion to auxiliary bishop of Malta in 2012.
"Let he who is without sin cast the first stone," he told the Italian daily La Stampa in an interview published Monday.
But he added: "The real scandal is not to have reported the abuses. Perceptions have changed. Silence has become scandal. And the credit goes to [the pope]."
Support groups for victims of pedophile priests in the United States, Belgium and Ireland say Mahony as well as former Philadelphia archbishop Justin Francis Rigali, Belgian Cardinal Godfried Danneels and Ireland's Sean Brady should be barred from voting because of their records in the scandals.
On Sunday, according to the British weekly the Observer, another cardinal, Britain's Keith O'Brien, has been reported to the Vatican over claims of inappropriate behavior lodged by four people.
A Vatican communications aide, Greg Burke, said in an interview published Monday that the media "could try" to influence the conclave, adding that "some can be truly odious."
The Vatican's Secretariat of State—the government of the Catholic Church—took the unusual step on Saturday of issuing a statement condemning "completely false news stories" as an attempt to influence the secret conclave.
"The negative effects of a work of imagination and approximation directly affect people's lives and reputations," Burke told the Rome daily Il Messagero, adding: "People have suffered because of the documents stolen" in the so-called Vatileaks scandal.
"There are people who lost everything while some journalists profited immensely," he said.
Benedict's butler Paolo Gabriele leaked secret papal memos to a journalist revealing a series of alleged fraud scandals in the Vatican and intrigues between rival groups of cardinals.
The pope later pardoned Gabriele, who had been sentenced to 18 months in jail, but banished him from the Vatican.