Eight people are being questioned over the weekend murder of a young man and his new girlfriend.
As investigating officers released one man without charge, another suspect, a 49-year-old man, was arrested in Limerick city.
Three other men and four women remain in custody over the double killing of criminal Des Kelly, 23, and Breda Waters, 28, on a housing estate in Limerick's Southill area.
Two men are believed to have carried out the murders.
The latest suspect is being detained at Mayorstone Garda Station under Section 50 of the Criminal Justice Act 2007.
It is believed the attackers called at the house at Castle Oaks View in the troubled O'Malley Park, where Kelly lived with his mother, at around 9am on Sunday.
They were allowed into the house through the back door where Kelly, a father of three young children, was shot at least once in the head at close range with a handgun.
The gangsters then went after Ms Waters, who also had three children and had started dating Kelly recently, and shot her in the head in an upstairs bedroom.
Kelly's sister and his two-month-old baby were in the house at the time but it is thought the gunmen did not realise anyone else was there.
It is believed Kelly might have fallen out with drug gangs over unpaid debts or missing drugs.