The Labour Party has backed a call for an independent inquiry into the unsolved murders of two woman in Grangegorman, Dublin in March 1997.
Sylvia Shiels (58) and Mary Callinan (61) were stabbed to death in their sheltered housing accommodation at St Brendan's psychiatric hospital.
Despite two separate confessions to the murders no one has been successfully prosecuted.
Yesterday a solicitor representing Ms Shiels's sister, Ms Stella Nolan, said he had sent a letter to the Minister for Justice formally requesting an inquiry.
A spokeswoman for the Department of Justice told ireland.com today that "on receipt of the correspondence it will be considered by the Minister".
The Labour Party's justice spokesman, Mr Joe Costello, today added his voice to the call for a public inquiry.
Mr Costello said the questions surrounding the conduct of the original investigation were so serious that "the Minister for Justice has to give serious consideration to revisiting the case to clear up the allegations that linger."
Mr Costello said: "Serious questions have to be asked about the conduct of the gardaí throughout."
"The only appropriate forum for this to be done is through an independent inquiry."
"The Minister for Justice must accede to the request for such an inquiry as the only means of appropriately investigated a case that existing legal mechanisms have been unable to solve."
The DPP has never explained why a prosecution was not taken against Mark Nash, who confessed to the attacks when he was picked up for the double murder of a couple in Roscommon. He subsequently withdrew the statement. He is now in Arbour Hill prison for the murder of Carl and Catherine Doyle.
Dean Lyons, a homeless drug addict, had earlier confessed to the Grangegorman killings, and spent time in custody, but question marks hung over the confession. The charges against him were dropped, and he moved to England, where he died in 2000.
