A complainant against then-Sinn Féin TD Brian Stanley was left “traumatised and distressed” by his actions, Mary Lou McDonald has told the Dail.
Ms McDonald’s comments came as she sought to defend the party’s record on a series of scandals.
At the weekend, it emerged that Laois-Offaly TD Mr Stanley had resigned from the party and would run as an independent in the next general election.
He had resigned after the party contacted him about the preliminary findings of an internal probe into a complaint made against him and a “serious” counter-allegation he raised during the process.
While Ms McDonald and Mr Stanley both said the original complaint was not of a criminal nature, Sinn Féin has since referred both matters to An Garda Síochána.
Mr Stanley has claimed he was subjected to a “character assassination” by a clique within the party and likened its processes to a kangaroo court.
In the Dáil on Tuesday, Ms McDonald said the circumstances around Mr Stanley’s resignation from Sinn Féin are “very, very serious”.
She said: “The complaint relates to an incident that took place in October 2023 and relates to Deputy Stanley’s personal behaviour – leaving the complainant, in her words, traumatised and distressed.
“In the course of the inquiry into the complaint against Deputy Stanley, he raised a counter allegation against the complainant and a very serious one. The allegation caused deep concern, and Deputy Stanley was advised that he should go to the gardaí. He chose not to.
“Deputy Stanley’s allegation also dates back to the incident of October 2023.”
Sinn Féin referred both matters to gardaí on Sunday after the completion of a preliminary report from its internal inquiry.
She said: “Deputy Stanley is responsible for his behaviour and he must account for it. For our part, Sinn Féin responded to a serious complaint and counter allegation in a correct and fair manner.”
Separately, Ms McDonald said the recent resignation of Patricia Ryan was related to a contested selection convention in Kildare South before the general election.
