Rome, October 25 - The pope's former butler Paolo Gabriele could be pardoned if he makes a "sincere request for forgiveness" from Benedict XVI, Vatican spokesman Federico Lombardi said on Thursday. Gabriele's 18-month sentence for stealing private papal correspondence became executive on Thursday and he is set to pass his first night in a Vatican prison cell. Earlier this week Lombardi said the pope had the power to pardon Gabriele and was "very likely" to use it. Gabriele has been under house arrest with his family since being sentenced. Lombardi said that Gabriele had to recognize the gravity of his crime and "make a sincere request for forgiveness from the Supreme Pontiff and those who were unjustly offended".