One of the three attackers shot dead in London on Saturday night was carrying an Irish residency card and had lived in Dublin, according to a report Monday by Ireland's national broadcaster RTE.
Citing security sources, RTE said this was 30-year-old Rachid Redouane, one of the two men identified by British police earlier Monday.
London's Metropolitan Police Service said Redouane also used the name Rachid Elkhdar, sometimes gave a different date of birth putting his age at 25 and "claimed to be Moroccan and Libyan".
RTE quoted police saying he was "of Moroccan and Libyan descent" and had married a British woman in Ireland in 2011 before moving to Britain.
"Irish detectives suspect he may have been married to a 38-year-old woman currently in custody in the UK," the report said.
The Guardian reported that he was a pastry chef.
The Irish police force is "providing every assistance to our colleagues in the London Metropolitan Police in relation to the terror attack in London," it told AFP in a statement.
"We will process all requests from the UK authorities in relation to enquiries into individuals, identities or any other matter," the statement added.
RTE said officers at the Garda (police) National Immigration Bureau (GNIB) were checking records to establish the residency of the man and his marital status while he was living in the country.
The nature of the card has not been divulged but sources said it was most likely to have been either a GNIB identity card or an Irish EU Fam Card, a type of residency card for non-EU citizens linked to an EU resident in Ireland.
Non-EU citizens who move to Ireland must register with immigration authorities on arrival, and if they stay for more than three months they must apply for a GNIB identity card and carry it with them at all times.
Alternatively, the man may have been granted an EU Fam Card on the basis of his relationship with an EU citizen in Ireland.
The Irish police are responsible for national security in the country, which does not have a separate intelligence service.