Gardaí have confirmed that an arm found on Dollymount Strand belonged to James Nolan, a 46-year-old convicted rapist and burglar who was released from prison last November.
Mr Nolan has not been reported missing but has not been seen since his release.
Gardaí are trying to establish his whereabouts but fear he could have been killed.
The investigation began following the discovery of the arm on Dollymount Strand in Dublin on 8 February last.
A DNA sample was taken, sent to Interpol and British police identified it as that of Nolan.
His DNA had been maintained on a database in the UK after he had been arrested there. There is no DNA database in Ireland.
Nolan was sentenced to 14 years for rape in 1986.
Following his release from prison, he was jailed again for 18 months in 2009 for burglary.
He was released from the Midlands Prison on 22 November 2010 but his whereabouts are unknown. His parents have passed away and his family in Finglas have not seen him.
Gardaí are now trying to establish the circumstances in which he lost his arm and although he could still be alive, they fear he could have been killed.