Tom and Molly Martens are set to be released from prison in the US this week after serving one month of a seven-month sentence.
The father and daughter both entered guilty pleas to the voluntary manslaughter of Jason Corbett (39) in October.
The Limerick man was beaten to death with a baseball bat and a concrete paving slab in his North Carolina home in 2015.
Martens and her father were originally convicted of his murder; however, the North Carolina Supreme Court later ordered a retrial.
They accepted charges of voluntary manslaughter as part of a plea deal.
Tom Martens will be released tomorrow, while Molly Martens will leave prison on Wednesday.
Irish Independent Southern Correspondent Ralph Riegel told Newstalk it is a dramatic development.
"It's quite a shocking development, given that the Irish family had been led to believe that they would not be released from custody until next May or June," he said.
"The North Carolina Department of Corrections have confirmed the release dates, but what they have not done is offered any explanation for why they are being released after just one month of a seven month sentence.
"Both Tom and Molly had been convicted of Mr Corbett's second degree murder in August 2017, and they had served three years and eight months of a 20 to 25 year prison sentence.
"That conviction and sentence was overturned on appeal".
'Pressure on prison spaces'
Mr Riegel said prison space and a lack of previous convictions seems to be contributing to the latest decesion.
"Both Tom and Molly pleaded guilty to voluntary manslaughter charges and were jailed for a further seven months," he said.
"They will now serve just four weeks of that seven-month additional term.
"We understand that it is linked to pressure on prison spaces in North Carolina, allied to the nature of their sentence and their previous lack of convictions."
Mr Riegel said the Corbett family feels very let down.
"They have consistently said that they put their faith in the justice system in North Carolina," he said.
"I know that they feel very badly let down today.
"I think they feel particularly upset given that they were not informed by any of the agencies in North Carolina of this development," he added.
Mr Riegel said the Corbett family learned of the decesion to release the Martens from an Irish media outlet.