Maybe they suddenly became aware of their sin, felt contrition, realized they were in a confessional, and said to each other, "Hey, when in Rome...."
So here's the word from the eternal city itself:
ROME (Reuters) - An Italian couple who were caught having sex in a church confessional box while morning Mass was being said have repented and made peace with the local bishop.
The couple, in their early 30s, were detained by police earlier this month after they had made love in the confessional box in the cathedral in northern Cesena. They were cautioned for obscene acts in public and disturbing a religious function.
Their lawyer said they had been drinking all night and realised they had gone too far.
The full story is here.
p.s. See? I told you Catholics like sex.