A statement said that Pope Francis had agreed with the decision but did not say whether it was the pope's idea that O'Brien should leave for what the Vatican said would be "several months for the purpose of spiritual renewal, prayer and penance".
The statement did not say where the Cardinal was going.
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From the time three bodies were found at a house in Oxfordshire to when prime murder suspect Jed Allen was found dead in woodland.
Mostly cloudy overnight, but as low pressure systems feed in as the week goes on an unsettled period can be expected.
The hunt for murder suspect Jed Allen has ended after police found his body two days after discovering his mother, stepdad and sister dead.