The Prison Service is investigating how Massey managed to elude staff.
A Prison Service spokesman said:
This continues to be the subject of a thorough ongoing investigation and Mr Massey will be returned to prison custody as soon as possible.
We always press for the heaviest penalties for those who escape or attempt to escape.
More top news
Early cloud and rain will slowly clear away from southeast England and East Anglia.
A Cornish fish restaurant has been named the best in the UK - knocking Cumbria's L'Enclume into second place after five years at the top.
There "will not be a war again on the Korean Peninsula", South Korea's President Moon Jae-in has said.