The Taoiseach has called on Sinn Féin to provide more information on its knowledge of former party councillor Jonathan Dowdall's actions, following the conclusion of the Regency murder trial.
Mr Varadkar also said that Sinn Féin is not "guilty by association" with the former councillor, who is in prison for his involvement in the 2016 Regency Hotel murder.
Yesterday, Gerard 'The Monk' Hutch was found not guilty of the murder of David Byrne, the Kinahan gang member who was shot dead at the Regency Hotel in 2016.
Sinn Féin leader Mary Lou McDonald issued a statement after the Regency verdict to say Dowdall "should never have been a member of Sinn Fein" given what he "would become involved in".
Dowdall joined Sinn Féin in mid-2013 and resigned from the party in February 2015.
He later admitted to falsely imprisoning and threatening to kill a man in January 2015.
The Special Criminal Court judgment dismissed evidence given by Dowdall in the Regency trial.
Dowdall is serving a four-year sentence for facilitating Mr Byrne's murder in 2016.
Speaking in the Dáil today, Mr Varadkar said: "I don't think for a second that Sinn Féin is in any way responsible for Dowdall's actions.
"I know it can be difficult to vet candidates and I don't believe in guilt by association."
But he added that many convictions would not have been possible without the non-jury Special Criminal Court, and called on Sinn Féin to emphatically support it.
"I do want to call on Sinn Féin, to call on the leaders of Sinn Féin in particular, to affirm that they will vote for the renewal of the Special Criminal Court in June - not an abstention, not not turning up - that you will vote for the retention of the Special Criminal Court."
Mr Varadkar said in the Dáil that a €1,000 donation from Dowdall to Sinn Féin should be returned and information on other donations made available, along with "Sinn Féin's knowledge of Mr Dowdall's actions".
Mr Varadkar thanked "the gardaí, the DPP and the courts" for their work in the Regency murder trial.
There has been "no murder related to a criminal gang feud in Ireland for five years now", he said, and hopes that this continues.
Earlier today, Sinn Féin's spokesperson on housing Eoin Ó Broin said the party has made it very clear that Dowdall should never have been a member of the party.
"We simply didn't know and had we known, he would not have been a member of our party," Mr Ó Broin said.
Speaking on RTÉ's Morning Ireland, Mr Ó Broin added that Dowdall was not questioned by party officials about allegations of criminal investigations - as Dowdall had claimed.
He said that Dowdall was involved in organised crime and the party "has no truck with that".
Ms McDonald had described as "false and deeply offensive" comments made by Dowdall during the course of the trial of Gerard Hutch.
